{"id":4724,"date":"2019-06-24T14:26:42","date_gmt":"2019-06-24T14:26:42","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/9-4-3\/"},"modified":"2023-11-30T18:49:00","modified_gmt":"2023-11-30T18:49:00","slug":"9-4-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/9-4-3\/","title":{"raw":"7.6 Human Body Cavities","rendered":"7.6 Human Body Cavities"},"content":{"raw":"&nbsp;\r\n<div>\r\n\r\n&nbsp;\r\n\r\n[caption id=\"attachment_2920\" align=\"aligncenter\" width=\"400\"]<img class=\"wp-image-2920\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2020\/04\/Brain_-_Lobes-2.png\" alt=\"Brain Lobes\" width=\"400\" height=\"278\" \/> <em>Figure 7.6.1 The human brain. <\/em>[\/caption]\r\n\r\n<strong>Contain the Brain<\/strong>\r\n\r\n<\/div>\r\nYou probably recognize the colourful object in this photo (Figure 7.6.1) as a human brain. The brain is arguably the most important organ in the human body. Fortunately for us, the brain has its own special \u201ccontainer,\u201d called the cranial cavity. The cranial cavity enclosing the brain is just one of several cavities in the human body that form \u201ccontainers\u201d for vital organs.\r\n<div>\r\n\r\n<strong>What Are Body Cavities?<\/strong>\r\n\r\n<\/div>\r\nThe human body, like that of many other multicellular organisms, is divided into a number of body cavities. A\u00a0<strong>[pb_glossary id=\"5911\"]body cavity[\/pb_glossary]<\/strong> is a fluid-filled space inside the body that holds and protects internal organs. Human body cavities are separated by membranes and other structures. The two largest human body cavities are the ventral cavity and dorsal cavity. These two body cavities are subdivided into smaller body cavities. Both the dorsal and ventral cavities and their subdivisions are shown in the Figure 7.6.2 diagram.\r\n\r\n[caption id=\"attachment_2919\" align=\"aligncenter\" width=\"503\"]<img class=\"size-full wp-image-2919\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/body_cavities-en.svg_-2.png\" alt=\"Body Cavities\" width=\"503\" height=\"607\" \/> <em>Figure 7.6.2 Human body cavities.<\/em>[\/caption]\r\n\r\n<div>\r\n\r\n<strong>Ventral Cavity<\/strong>\r\n\r\n<\/div>\r\nThe\u00a0<strong>[pb_glossary id=\"2923\"]ventral cavity[\/pb_glossary]<\/strong>\u00a0is at the anterior (or front) of the trunk. Organs contained within this body cavity include the lungs, heart, stomach, intestines, and reproductive organs. The ventral cavity allows for considerable changes in the size and shape of the organs\u00a0inside\u00a0as they perform their functions.\u00a0Organs such as the lungs, stomach, or uterus, for example, can expand or contract without distorting other tissues or disrupting the activities of nearby organs.\r\n\r\nThe ventral cavity is subdivided into the [pb_glossary id=\"2925\"]thoracic[\/pb_glossary] and [pb_glossary id=\"5857\"]abdominopelvic cavities[\/pb_glossary].\r\n<ul>\r\n \t<li>The\u00a0<strong>[pb_glossary id=\"2925\"]thoracic cavity[\/pb_glossary]<\/strong>\u00a0fills the chest and is subdivided into two pleural cavities and the pericardial cavity. The pleural cavities hold the lungs, and the pericardial cavity holds the heart.<\/li>\r\n \t<li>The\u00a0<strong>[pb_glossary id=\"5857\"]abdominopelvic cavity[\/pb_glossary]<\/strong>\u00a0fills the lower half of the trunk and is subdivided into the abdominal cavity and the pelvic cavity. The abdominal cavity holds digestive organs and the kidneys, and the pelvic cavity holds reproductive organs and organs of excretion.<\/li>\r\n<\/ul>\r\n<div>\r\n\r\n<strong>Dorsal Cavity<\/strong>\r\n\r\n<\/div>\r\nThe\u00a0<strong>[pb_glossary id=\"5975\"]dorsal cavity[\/pb_glossary]<\/strong>\u00a0is at the posterior (or back) of the body, including both the head and the back of the trunk. The dorsal cavity is subdivided into the cranial and spinal cavities.\r\n<ul>\r\n \t<li>The\u00a0<strong>[pb_glossary id=\"5961\"]cranial cavity[\/pb_glossary]<\/strong>\u00a0fills most of the upper part of the skull and contains the brain.<\/li>\r\n \t<li>The\u00a0<strong>[pb_glossary id=\"2928\"]spinal cavity[\/pb_glossary]<\/strong>\u00a0is a very long, narrow cavity inside the vertebral column. It runs the length of the trunk and contains the spinal cord.<\/li>\r\n<\/ul>\r\nThe brain and spinal cord are protected by the bones of the skull and the vertebrae of the spine. They are further protected by the\u00a0<strong>[pb_glossary id=\"2929\"]meninges[\/pb_glossary],<\/strong>\u00a0a three-layer membrane that encloses the brain and spinal cord. A thin layer of\u00a0<strong>[pb_glossary id=\"5939\"]cerebrospinal fluid[\/pb_glossary]<\/strong>\u00a0is maintained between two of the meningeal layers. This clear fluid is produced by the brain, and it provides extra protection and cushioning for the brain and spinal cord.\r\n<div>\r\n\r\n<strong>Feature: My Human Body<\/strong>\r\n\r\n<\/div>\r\nThe meninges membranes that protect the brain and spinal cord inside their cavities may become inflamed, generally due to a bacterial or viral infection. This condition is called <a href=\"https:\/\/www.mayoclinic.org\/diseases-conditions\/meningitis\/symptoms-causes\/syc-20350508\">meningitis<\/a>, and it can lead to serious long-term consequences such as deafness, epilepsy, or cognitive deficits, especially if not treated quickly. Meningitis can also rapidly become life-threatening, so it is classified as a medical emergency.\r\n\r\nLearning the symptoms of meningitis may help you or a loved one get prompt medical attention if you ever develop the disease. Common symptoms include fever, headache, and neck stiffness. Other symptoms include confusion or altered consciousness, vomiting, and an inability to tolerate light or loud noises. Young children often exhibit less specific symptoms, such as irritability, drowsiness, or poor feeding.\r\n\r\nMeningitis is diagnosed with a lumbar puncture (commonly known as a \"spinal tap\"), in which a needle is inserted into the spinal canal to collect a sample of [pb_glossary id=\"5939\"]cerebrospinal fluid[\/pb_glossary]. The fluid is analyzed in a medical lab for the presence of pathogens. If meningitis is diagnosed, treatment consists of antibiotics and sometimes antiviral drugs. Corticosteroids may also be administered to reduce inflammation and the risk of complications (such as brain damage). Supportive measures such as IV fluids may also be provided.\r\n\r\nSome types of meningitis can be prevented with a vaccine. Ask your health care professional whether you have had the vaccine or should get it. Giving antibiotics to people who have had significant exposure to certain types of meningitis may reduce their risk of developing the disease. If someone you know is diagnosed with meningitis and you are concerned about contracting the disease yourself, see your doctor for advice.\r\n<div class=\"textbox textbox--key-takeaways\"><header class=\"textbox__header\">\r\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.6 Summary<\/span><\/h1>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<ul>\r\n \t<li>The human body is divided into a number of body cavities, fluid-filled spaces in the body that hold and protect internal organs. The two largest human body cavities are the ventral cavity and dorsal cavity.<\/li>\r\n \t<li>The ventral cavity is at the anterior (or front) of the trunk. It is subdivided into the thoracic cavity and abdominopelvic cavity.<\/li>\r\n \t<li>The dorsal cavity is at the posterior (or back) of the body, and includes the head and the back of the trunk. It is subdivided into the cranial cavity and spinal cavity.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox textbox--exercises\"><header class=\"textbox__header\">\r\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.6 Review Questions<\/span><\/h1>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<ol>\r\n \t<li style=\"list-style-type: none;\">\r\n<ol>\r\n \t<li>What is a body cavity?<\/li>\r\n \t<li>Compare and contrast the ventral and dorsal body cavities.<\/li>\r\n \t<li>Identify the subdivisions of the ventral cavity, and the organs each contains.<\/li>\r\n \t<li>Describe the subdivisions of the dorsal cavity and their contents.<\/li>\r\n \t<li>Identify and describe all the tissues that protect the brain and spinal cord.<\/li>\r\n \t<li>What do you think might happen if fluid were to build up excessively in one of the body cavities?<\/li>\r\n \t<li>Explain why a woman\u2019s body can accommodate a full-term fetus during pregnancy without\u00a0damaging\u00a0her internal organs.<\/li>\r\n \t<li>Which body cavity does the needle enter in a lumbar puncture?<\/li>\r\n \t<li>What are the names given to the three body cavity divisions where the heart is located?What are the names given to the three body cavity divisions where the kidneys are located?<\/li>\r\n \t<li>[h5p id=\"544\"]<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox textbox--examples\"><header class=\"textbox__header\">\r\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.6 Explore More<\/span><\/h1>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=IaQdv_dBDqM\r\n<p style=\"text-align: center;\">Why is meningitis so dangerous? - Melvin Sanicas, TED-Ed, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<h2>Attributions<\/h2>\r\n<strong>Figure 7.6.1<\/strong>\r\n\r\n<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Brain_-_Lobes.png\" rel=\"cc:attributionURL\">Brain Lobes<\/a> by John A Beal, Department of Cellular Biology &amp; Anatomy, Louisiana State University Health Sciences Center Shreveport on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.5\/deed.en\" rel=\"license\">CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5\/deed.en) license.\r\n\r\n<strong>Figure 7.6.2<\/strong>\r\n\r\n<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Scheme_body_cavities-en.svg\" rel=\"cc:attributionURL\">body_cavities-en.svg<\/a> by <a class=\"extiw\" title=\"w:User:Mysid\" href=\"https:\/\/en.wikipedia.org\/wiki\/User:Mysid\">Mysid<\/a> (SVG) on Wikimedia Commons is in the <a class=\"extiw\" title=\"w:en:Public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/en:Public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original by US National Cancer Institute [<a href=\"https:\/\/training.seer.cancer.gov\/module_anatomy\/unit1_3_terminology3_cavities.html\">NCI].<\/a>)\r\n<h2>References<\/h2>\r\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Meningitis. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/meningitis\/symptoms-causes\/syc-20350508<\/p>\r\n<p class=\"hanging-indent\">TED-Ed. (2018, November 19). Why is meningitis so dangerous? - Melvin Sanicas. YouTube. https:\/\/www.youtube.com\/watch?v=IaQdv_dBDqM&amp;feature=youtu.be<\/p>\r\n&nbsp;","rendered":"<p>&nbsp;<\/p>\n<div>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_2920\" aria-describedby=\"caption-attachment-2920\" style=\"width: 400px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2920\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2020\/04\/Brain_-_Lobes-2.png\" alt=\"Brain Lobes\" width=\"400\" height=\"278\" \/><figcaption id=\"caption-attachment-2920\" class=\"wp-caption-text\"><em>Figure 7.6.1 The human brain. <\/em><\/figcaption><\/figure>\n<p><strong>Contain the Brain<\/strong><\/p>\n<\/div>\n<p>You probably recognize the colourful object in this photo (Figure 7.6.1) as a human brain. The brain is arguably the most important organ in the human body. Fortunately for us, the brain has its own special \u201ccontainer,\u201d called the cranial cavity. The cranial cavity enclosing the brain is just one of several cavities in the human body that form \u201ccontainers\u201d for vital organs.<\/p>\n<div>\n<p><strong>What Are Body Cavities?<\/strong><\/p>\n<\/div>\n<p>The human body, like that of many other multicellular organisms, is divided into a number of body cavities. A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5911\">body cavity<\/a><\/strong> is a fluid-filled space inside the body that holds and protects internal organs. Human body cavities are separated by membranes and other structures. The two largest human body cavities are the ventral cavity and dorsal cavity. These two body cavities are subdivided into smaller body cavities. Both the dorsal and ventral cavities and their subdivisions are shown in the Figure 7.6.2 diagram.<\/p>\n<figure id=\"attachment_2919\" aria-describedby=\"caption-attachment-2919\" style=\"width: 503px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-2919\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/body_cavities-en.svg_-2.png\" alt=\"Body Cavities\" width=\"503\" height=\"607\" \/><figcaption id=\"caption-attachment-2919\" class=\"wp-caption-text\"><em>Figure 7.6.2 Human body cavities.<\/em><\/figcaption><\/figure>\n<div>\n<p><strong>Ventral Cavity<\/strong><\/p>\n<\/div>\n<p>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2923\">ventral cavity<\/a><\/strong>\u00a0is at the anterior (or front) of the trunk. Organs contained within this body cavity include the lungs, heart, stomach, intestines, and reproductive organs. The ventral cavity allows for considerable changes in the size and shape of the organs\u00a0inside\u00a0as they perform their functions.\u00a0Organs such as the lungs, stomach, or uterus, for example, can expand or contract without distorting other tissues or disrupting the activities of nearby organs.<\/p>\n<p>The ventral cavity is subdivided into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2925\">thoracic<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5857\">abdominopelvic cavities<\/a>.<\/p>\n<ul>\n<li>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2925\">thoracic cavity<\/a><\/strong>\u00a0fills the chest and is subdivided into two pleural cavities and the pericardial cavity. The pleural cavities hold the lungs, and the pericardial cavity holds the heart.<\/li>\n<li>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5857\">abdominopelvic cavity<\/a><\/strong>\u00a0fills the lower half of the trunk and is subdivided into the abdominal cavity and the pelvic cavity. The abdominal cavity holds digestive organs and the kidneys, and the pelvic cavity holds reproductive organs and organs of excretion.<\/li>\n<\/ul>\n<div>\n<p><strong>Dorsal Cavity<\/strong><\/p>\n<\/div>\n<p>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5975\">dorsal cavity<\/a><\/strong>\u00a0is at the posterior (or back) of the body, including both the head and the back of the trunk. The dorsal cavity is subdivided into the cranial and spinal cavities.<\/p>\n<ul>\n<li>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5961\">cranial cavity<\/a><\/strong>\u00a0fills most of the upper part of the skull and contains the brain.<\/li>\n<li>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2928\">spinal cavity<\/a><\/strong>\u00a0is a very long, narrow cavity inside the vertebral column. It runs the length of the trunk and contains the spinal cord.<\/li>\n<\/ul>\n<p>The brain and spinal cord are protected by the bones of the skull and the vertebrae of the spine. They are further protected by the\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2929\">meninges<\/a>,<\/strong>\u00a0a three-layer membrane that encloses the brain and spinal cord. A thin layer of\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5939\">cerebrospinal fluid<\/a><\/strong>\u00a0is maintained between two of the meningeal layers. This clear fluid is produced by the brain, and it provides extra protection and cushioning for the brain and spinal cord.<\/p>\n<div>\n<p><strong>Feature: My Human Body<\/strong><\/p>\n<\/div>\n<p>The meninges membranes that protect the brain and spinal cord inside their cavities may become inflamed, generally due to a bacterial or viral infection. This condition is called <a href=\"https:\/\/www.mayoclinic.org\/diseases-conditions\/meningitis\/symptoms-causes\/syc-20350508\">meningitis<\/a>, and it can lead to serious long-term consequences such as deafness, epilepsy, or cognitive deficits, especially if not treated quickly. Meningitis can also rapidly become life-threatening, so it is classified as a medical emergency.<\/p>\n<p>Learning the symptoms of meningitis may help you or a loved one get prompt medical attention if you ever develop the disease. Common symptoms include fever, headache, and neck stiffness. Other symptoms include confusion or altered consciousness, vomiting, and an inability to tolerate light or loud noises. Young children often exhibit less specific symptoms, such as irritability, drowsiness, or poor feeding.<\/p>\n<p>Meningitis is diagnosed with a lumbar puncture (commonly known as a &#8220;spinal tap&#8221;), in which a needle is inserted into the spinal canal to collect a sample of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_5939\">cerebrospinal fluid<\/a>. The fluid is analyzed in a medical lab for the presence of pathogens. If meningitis is diagnosed, treatment consists of antibiotics and sometimes antiviral drugs. Corticosteroids may also be administered to reduce inflammation and the risk of complications (such as brain damage). Supportive measures such as IV fluids may also be provided.<\/p>\n<p>Some types of meningitis can be prevented with a vaccine. Ask your health care professional whether you have had the vaccine or should get it. Giving antibiotics to people who have had significant exposure to certain types of meningitis may reduce their risk of developing the disease. If someone you know is diagnosed with meningitis and you are concerned about contracting the disease yourself, see your doctor for advice.<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.6 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>The human body is divided into a number of body cavities, fluid-filled spaces in the body that hold and protect internal organs. The two largest human body cavities are the ventral cavity and dorsal cavity.<\/li>\n<li>The ventral cavity is at the anterior (or front) of the trunk. It is subdivided into the thoracic cavity and abdominopelvic cavity.<\/li>\n<li>The dorsal cavity is at the posterior (or back) of the body, and includes the head and the back of the trunk. It is subdivided into the cranial cavity and spinal cavity.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.6 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li>What is a body cavity?<\/li>\n<li>Compare and contrast the ventral and dorsal body cavities.<\/li>\n<li>Identify the subdivisions of the ventral cavity, and the organs each contains.<\/li>\n<li>Describe the subdivisions of the dorsal cavity and their contents.<\/li>\n<li>Identify and describe all the tissues that protect the brain and spinal cord.<\/li>\n<li>What do you think might happen if fluid were to build up excessively in one of the body cavities?<\/li>\n<li>Explain why a woman\u2019s body can accommodate a full-term fetus during pregnancy without\u00a0damaging\u00a0her internal organs.<\/li>\n<li>Which body cavity does the needle enter in a lumbar puncture?<\/li>\n<li>What are the names given to the three body cavity divisions where the heart is located?What are the names given to the three body cavity divisions where the kidneys are located?<\/li>\n<li>\n<div id=\"h5p-544\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-544\" class=\"h5p-iframe\" data-content-id=\"544\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Body Cavities\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.6 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Why is meningitis so dangerous? - Melvin Sanicas\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/IaQdv_dBDqM?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p style=\"text-align: center;\">Why is meningitis so dangerous? &#8211; Melvin Sanicas, TED-Ed, 2018.<\/p>\n<\/div>\n<\/div>\n<h2>Attributions<\/h2>\n<p><strong>Figure 7.6.1<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Brain_-_Lobes.png\" rel=\"cc:attributionURL\">Brain Lobes<\/a> by John A Beal, Department of Cellular Biology &amp; Anatomy, Louisiana State University Health Sciences Center Shreveport on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.5\/deed.en\" rel=\"license\">CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5\/deed.en) license.<\/p>\n<p><strong>Figure 7.6.2<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Scheme_body_cavities-en.svg\" rel=\"cc:attributionURL\">body_cavities-en.svg<\/a> by <a class=\"extiw\" title=\"w:User:Mysid\" href=\"https:\/\/en.wikipedia.org\/wiki\/User:Mysid\">Mysid<\/a> (SVG) on Wikimedia Commons is in the <a class=\"extiw\" title=\"w:en:Public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/en:Public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain). (Original by US National Cancer Institute [<a href=\"https:\/\/training.seer.cancer.gov\/module_anatomy\/unit1_3_terminology3_cavities.html\">NCI].<\/a>)<\/p>\n<h2>References<\/h2>\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Meningitis. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/meningitis\/symptoms-causes\/syc-20350508<\/p>\n<p class=\"hanging-indent\">TED-Ed. (2018, November 19). Why is meningitis so dangerous? &#8211; Melvin Sanicas. YouTube. https:\/\/www.youtube.com\/watch?v=IaQdv_dBDqM&amp;feature=youtu.be<\/p>\n<p>&nbsp;<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_4724_5911\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_5911\"><div tabindex=\"-1\"><p>A fluid-filled space inside the body that holds and protects internal organs.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_2923\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_2923\"><div tabindex=\"-1\"><p>Created by: CK-12\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_353\" aria-describedby=\"caption-attachment-353\" style=\"width: 824px\" class=\"wp-caption alignnone\"><img class=\" wp-image-351\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/AMY1gene.png\" alt=\"\" width=\"824\" height=\"313\"><figcaption id=\"caption-attachment-353\" class=\"wp-caption-text\"><em>Figure 5.6.1 DNA stores information in the sequence of nitrogenous bases. This works similarly to computer coding.<\/em><\/figcaption><\/figure>\n<h1>Can You Code?<\/h1>\n<p>If someone asks you whether you can code, you probably assume they are referring to computer code. The image in Figure 5.6.1 represents an important code that you use all the time \u2014 but not with a computer! It's the genetic code, and it is used by your <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2223\">cells<\/a> to store information, as well as to make <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_519\">RNA<\/a> and proteins.<\/p>\n<div>\n<h1>What Is the Genetic Code?<\/h1>\n<\/div>\n<p>The genetic code consists of the sequence of nitrogen bases in a polynucleotide chain of DNA or RNA. The bases are adenine (A), cytosine (C), guanine (G), and thymine (T) (or uracil, U, in RNA). The four bases make up the \u201cletters\u201d of the genetic code. The letters are combined in groups of three to form code \u201cwords,\u201d called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2598\">codons<\/a>. Each codon stands for (encodes) one<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2279\"> amino acid<\/a>, unless it codes for a start or stop signal. There are 20 common amino acids in proteins. With four bases forming three-base codons, there are 64 possible codons. This is more than enough to code for the 20 amino acids. The genetic code is shown in Figure 5.6.2.<\/p>\n<figure id=\"attachment_353\" aria-describedby=\"caption-attachment-353\" style=\"width: 668px\" class=\"wp-caption alignnone\"><img class=\"wp-image-352\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/1000px-Aminoacids_table.png\" alt=\"\" width=\"668\" height=\"661\"><figcaption id=\"caption-attachment-353\" class=\"wp-caption-text\"><em>Figure 5.6.2 The Genetic Code (decoder). <\/em><\/figcaption><\/figure>\n<div>\n<p>To find the amino acid for a particular codon, find the first base in the codon in the centre of the circle in Figure 5.6.2, then the second base in the middle row out from the center, and finally the third base in the outer ring\u00a0 For example, CUG codes for leucine, AAG codes for lysine, and GGG codes for glycine. Try it out: Can you figure out what the codon AGC codes for?<\/p>\n<\/div>\n<h1>Reading the Genetic Code<\/h1>\n<p>If you find the codon AUG in Figure 5.6.2, you will see that it codes for the amino acid methionine. This codon is also the start codon that establishes the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2080\">reading frame<\/a> of the code.\u00a0 The start codon is a necessary tool in translation, since a single chromosome contains many genes.\u00a0 In order to transcribe and translate a gene for a specific protein, we need to know where in the DNA code to start \"reading\" the instructions.\u00a0 AUG signals the start of a reading frame. \u00a0After the AUG start codon, the next three bases are read as the second codon. The next three bases after that are read as the third codon, and so on. The sequence of bases is read, codon by codon, until a stop codon is reached. UAG, UGA, and UAA are all stop codons. They do not code for any amino acids.<\/p>\n<p>The importance of the reading frame is illustrated in the hypothetical situation\u00a0 below:<\/p>\n<p>The section of mRNA in Figure 5.6.3 is designed to create a chain of five specific amino acids.<\/p>\n<ul>\n<li>\u00a0In Option 1, a string of amino acids is created, but the chain does not have a stop codon, and so keeps on adding amino acids.\u00a0 This means the desired protein was not made.<\/li>\n<li>\u00a0 In Option 2, a stop codon was encountered and the amino acid chain was stopped after 3 amino acids. This means the desired protein was not made<\/li>\n<li>In Option 3, using the AUG start codon, a chain of five specific amino acids was successfully formed. Success!\u00a0 This was only possible because the start codon, AUG, specified the reading frame.<\/li>\n<\/ul>\n<figure id=\"attachment_353\" aria-describedby=\"caption-attachment-353\" style=\"width: 672px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-353\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Reading-Frame-e1585076712406.png\" alt=\"Illustrates the importance of the reading frame and the start codon in decoding mRNA\" width=\"672\" height=\"519\"><figcaption id=\"caption-attachment-353\" class=\"wp-caption-text\"><em>Figure 5.6.3 This segment of mRNA could be read a few ways, but only one of them produces the desired protein. The start codon, AUG, indicates where to begin the reading frame.<\/em><\/figcaption><\/figure>\n<div>\n<h1>Characteristics of the Genetic Code<\/h1>\n<\/div>\n<p>The genetic code has a number of important characteristics:<\/p>\n<ul>\n<li><strong>The genetic code is universal. <\/strong>All known living things have the same genetic code, which shows that all organisms share a common evolutionary history.<\/li>\n<li><strong>The genetic code is unambiguous. <\/strong>This means that each codon codes for just one amino\u00a0acid\u00a0(or start or stop). This is necessary so there is no question about which amino acid is correct.<\/li>\n<li><strong>The genetic code is redundant. <\/strong>This means that each amino acid is encoded by more than one codon. For example, in Figure 5.6.2, four codons code for the amino acid threonine. Redundancy in the code helps prevent errors in protein synthesis. If a base in a codon changes by accident, there is a good chance that it will still code for the same amino acid.<\/li>\n<\/ul>\n<div>\n<h1>Cracking the Code<\/h1>\n<\/div>\n<p>The double helix structure of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_277\">DNA<\/a>\u00a0was discovered in 1953. It took just eight more years to crack the genetic code. The scientist\u00a0primarily\u00a0responsible for deciphering the code was American biochemist <a href=\"https:\/\/en.wikipedia.org\/wiki\/Marshall_Warren_Nirenberg\">Marshall Nirenberg<\/a>, who worked at the National Institutes of Health in the United States. When Nirenberg began the\u00a0research\u00a0in 1959, the manner in which\u00a0proteins\u00a0are synthesized in\u00a0cells\u00a0was not well understood, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2212\">messenger\u00a0RNA<\/a>\u00a0had not yet been discovered. At that time, scientists didn't even know whether\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_277\">DNA<\/a>\u00a0or RNA was the molecule used as a template for\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2210\">protein synthesis<\/a>.\u00a0Nirenberg, along with a collaborator named <a href=\"https:\/\/en.wikipedia.org\/wiki\/J._Heinrich_Matthaei\">Heinrich Matthaei<\/a>, devised an ingenious\u00a0experiment\u00a0to determine which molecule \u2014 DNA or RNA \u2014 has this important role. They also began deciphering the genetic code.<\/p>\n<p>Nirenberg and Matthaei added the contents of bacterial\u00a0cells\u00a0to each of 20 test tubes. The cell contents provided the necessary \"machinery\" for the synthesis of a polypeptide molecule. The researchers also added all 20\u00a0amino acids\u00a0to the test tubes, with a different amino acid \"tagged\" by a radioactive\u00a0element\u00a0in each test tube. That way, if a polypeptide formed in a test tube, they would be able to tell which amino acid it contained. Then, they added synthetic RNA containing just one nitrogen\u00a0base\u00a0to all 20 test tubes. They used the base uracil in their first\u00a0experiment. They discovered that an RNA chain consisting only of uracil bases produces a polypeptide chain of the amino acid phenylalanine. This experiment showed that RNA (rather than DNA) is the template for\u00a0protein synthesis, but it also showed that a sequence of uracil bases codes for the amino acid phenylalanine. The year was 1961, and it was a momentous occasion. When Nirenberg presented the discovery at a scientific conference later that year, he received a standing ovation. As Nirenberg puts it, \"...for the next five years I became like a scientific rock star.\"<\/p>\n<p>After Nirenberg and Matthaei cracked the first word of the genetic code, they used similar experiments to show that each codon consists of three bases. Before long, they had discovered the codons for all 20 amino acids. In 1968, in recognition\u00a0of\u00a0this important achievement, Nirenberg was named a co-winner of the\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/Nobel_Prize_in_Physiology_or_Medicine\">Nobel Prize\u00a0in Physiology or Medicine<\/a>.<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.6 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>The genetic code consists of the sequence of nitrogen bases in a polynucleotide chain of DNA or RNA. The four bases make up the \"letters\" of the code. The letters are combined in groups of three to form code \"words\" known as codons, each of which encodes for one amino acid or a start or stop signal.<\/li>\n<li>AUG is the start codon, and it establishes the reading frame of the code. After the start codon, the next three bases are read as the second codon, the three bases after that as the third codon, and so on until a stop codon is reached.<\/li>\n<li>The genetic code is universal, unambiguous, and redundant.<\/li>\n<li>The genetic code was cracked in the 1960s, mainly by a series of ingenious experiments carried out by Marshall Nirenberg, who won a\u00a0Nobel Prize\u00a0for this achievement.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.6 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>Describe the genetic code and explain how it is \"read\"<\/li>\n<li>Identify three important characteristics of the genetic code.<\/li>\n<li>Summarize how the genetic code was deciphered.<\/li>\n<\/ol>\n<p><img class=\"alignnone wp-image-352\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/1000px-Aminoacids_table.png\" alt=\"\" width=\"395\" height=\"391\"><\/p>\n<ol>\n<li>Use the decoder above to answer the following questions:\n<ul>\n<li>Is the code from DNA or RNA? How do you know?<\/li>\n<li>Which amino acid does the codon CAA code for?<\/li>\n<li>What does UGA code for?<\/li>\n<li>Look at the codons that code for the amino acid glycine. How many of them are there and how are they similar and different?<\/li>\n<\/ul>\n<\/li>\n<li>\n<div id=\"h5p-66\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-66\" class=\"h5p-iframe\" data-content-id=\"66\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Codons\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.6 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>https:\/\/www.youtube.com\/watch?v=OSKwuOccAak&amp;feature=emb_logo<\/p>\n<p style=\"text-align: center\">Comparing DNA Sequences, Bozeman Science, 2012.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=LsEYgwuP6ko<\/p>\n<p style=\"text-align: center\">How to Read a Codon Chart, Amoeba Sisters, 2019.<\/p>\n<\/div>\n<\/div>\n<p><span style=\"font-size: 1.424em;font-weight: bold\">Attributions<\/span><\/p>\n<\/div>\n<p><strong>Figure 5.6.1<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:AMY1gene.png\" rel=\"cc:attributionURL\">AMY1gene<\/a> by unknown author from <i><a class=\"extiw\" title=\"en:National Science Foundation\" href=\"https:\/\/en.wikipedia.org\/wiki\/National_Science_Foundation\">National Science Foundation<\/a> on <\/i>Wikimedia Commons \u00a0is released into <i>the <a class=\"extiw\" title=\"w:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i><\/p>\n<p><strong>Figure 5.6.2<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Aminoacids_table.svg\" rel=\"cc:attributionURL\">Aminoacids table (<\/a>Adapted) by <a href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Mouagip\">Mouagip<\/a> <i>on <\/i>Wikimedia Commons \u00a0is released into <i>the <\/i><a class=\"extiw\" title=\"w:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/public_domain\">public domain<\/a><i>. <\/i>(Original: Codons sun (\"codesonne\" in German) by <a class=\"mw-userlink\" title=\"User:Onie~commonswiki\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Onie~commonswiki\">Onie~commonswiki<\/a>])<\/p>\n<p><strong>Figure 5.6.3<\/strong><\/p>\n<p>Reading Frame (3 Options) by Christine Miller is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\" rel=\"license\">CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.<\/p>\n<h2>References<\/h2>\n<p class=\"hanging-indent\">Amoeba Sisters. (2019, September 17). How to read a codon chart. YouTube. https:\/\/www.youtube.com\/watch?v=LsEYgwuP6ko&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Bozeman Science. (2012, September 15). Comparing DNA sequences. YouTube. https:\/\/www.youtube.com\/watch?v=OSKwuOccAak&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, July 2). Marshall Warren Nirenberg.\u00a0 In <i>Wikipedia.<\/i>\u00a0 https:\/\/en.wikipedia.org\/w\/index.php?title=Marshall_Warren_Nirenberg&amp;oldid=965562106<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_2925\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_2925\"><div tabindex=\"-1\"><p>Created by: CK-12\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_364\" aria-describedby=\"caption-attachment-364\" style=\"width: 400px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-2380\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/11027734365_3b6c9ec284_o-scaled-1.jpg\" alt=\"\" width=\"400\" height=\"264\"><figcaption id=\"caption-attachment-364\" class=\"wp-caption-text\"><em>Figure 5.8.1 Teenage Mutant Ninja Turtles Cosplay: Raphael and Michelangelo. <\/em><\/figcaption><\/figure>\n<p><span style=\"font-size: 1.602em;font-weight: bold\">Mutant Cosplay<\/span><\/p>\n<p>You probably recognize these costumed comic fans in Figure 5.8.1 as two of the four Teenage Mutant Ninja Turtles. Can a mutation really turn a reptile into an anthropomorphic superhero? Of course not \u2014 but mutations <em>can<\/em> often result in other drastic (but more realistic) changes in living things.<\/p>\n<div>\n<h1>What Are Mutations?<\/h1>\n<\/div>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2381\">Mutations<\/a><\/strong>\u00a0are random changes in the sequence of bases in\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_277\">DNA<\/a>\u00a0or\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_519\">RNA<\/a>. The word\u00a0<em>mutation<\/em>\u00a0may make you think of the <a href=\"https:\/\/en.wikipedia.org\/wiki\/Teenage_Mutant_Ninja_Turtles\">Ninja\u00a0Turtles<\/a>, but that's a misrepresentation of how most mutations work. First of all,\u00a0<em>everyone<\/em>\u00a0has mutations. In fact, most people have dozens (or even hundreds!) of mutations in their\u00a0DNA. Secondly, from an evolutionary perspective, mutations are essential. They are needed for evolution to occur because they are the ultimate source of all new\u00a0genetic variation\u00a0in any\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2424\">species<\/a>.<\/p>\n<div>\n<h1>Causes of Mutations<\/h1>\n<\/div>\n<p>Mutations have many possible causes. Some mutations seem to happen spontaneously, without any outside influence. They occur when errors are made during\u00a0DNA\u00a0replication or during the\u00a0transcription\u00a0phase of\u00a0protein synthesis. Other mutations are caused by environmental factors. Anything in\u00a0the environment\u00a0that can cause a mutation is known as a\u00a0<strong>mutagen<\/strong>. Examples of mutagens are shown in the figure\u00a0below.<\/p>\n<figure id=\"attachment_364\" aria-describedby=\"caption-attachment-364\" style=\"width: 899px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-363\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Mutagens.png\" alt=\"Examples of Radiation, chemicals and infectious agents: An mage of a sun icon and hand x-ray for UV and x-ray radiation; a picture of hands holding a cigarrette and a vape, 3 smokies on a grill (nitrates\/ nitrites and mutagenic BBQ chemicals) and a stylized image of a woman in a green acne face mask with benzoyl peroxide to represent chemicals. To represent infectious agents: an orange spherical virus as human papillomavirus (HPV) and a purple spirilla bacterium with flagella for Helicobacter Pylori - a bacteria spread through contaminated food.\" width=\"899\" height=\"697\"><figcaption id=\"caption-attachment-364\" class=\"wp-caption-text\"><em>Figure 5.8.2 Examples of Mutagens. Types of mutagens include radiation, chemicals, and infectious agents. Do you know of other examples of each type of mutagen shown here?<\/em><\/figcaption><\/figure>\n<div>\n<p>&nbsp;<\/p>\n<\/div>\n<p><span style=\"font-size: 1.602em;font-weight: bold\">Types of Mutations<\/span><\/p>\n<p>Mutations come in a variety of types. Two major categories of mutations are germline mutations and somatic mutations.<\/p>\n<ul>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2106\">Germline mutations<\/a> <\/strong>occur in gametes (the sex cells), such as eggs and\u00a0sperm. These mutations are especially significant because they can be transmitted to offspring, causing every cell in the offspring\u00a0to\u00a0carry\u00a0those\u00a0mutations.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2192\">Somatic mutations<\/a> <\/strong>occur in other\u00a0cells\u00a0of the body. These mutations may have little effect on the organism, because they are confined to just one cell and its daughter cells. Somatic mutations cannot be passed on to offspring.<\/li>\n<\/ul>\n<p>Mutations also differ in the way that the genetic material is changed. Mutations may change an entire chromosome, or they may alter just one or a few nucleotides.<\/p>\n<h2>Chromosomal Alterations<\/h2>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2388\">Chromosomal alterations<\/a><\/strong>\u00a0are mutations that change chromosome structure. They occur when a section of a chromosome breaks off and rejoins incorrectly, or otherwise does not rejoin at all. Possible ways in which these mutations can occur are illustrated in the figure\u00a0below.\u00a0Chromosomal alterations are very serious. They often result in the death of the organism in which they occur. If the organism survives, it may be affected in multiple ways. An example of a human disease caused by a chromosomal duplication is <a href=\"https:\/\/en.wikipedia.org\/wiki\/Charcot%E2%80%93Marie%E2%80%93Tooth_disease\">Charcot-Marie-Tooth disease type 1 (CMT1)<\/a>.\u00a0It is characterized by muscle weakness,\u00a0as well as\u00a0loss of muscle tissue and sensation. The most common cause of CMT1 is a duplication\u00a0of\u00a0part of\u00a0chromosome 17.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_364\" aria-describedby=\"caption-attachment-364\" style=\"width: 434px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-364 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Chromosomenmutationen.png\" alt=\"\" width=\"434\" height=\"487\"><figcaption id=\"caption-attachment-364\" class=\"wp-caption-text\"><em>Figure 5.8.3 Chromosomal alterations are major changes in the genetic material.<\/em><\/figcaption><\/figure>\n<div>\n<p><span style=\"font-size: 1.424em;font-weight: bold\">Point Mutations<\/span><\/p>\n<\/div>\n<p>A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2389\">point mutation<\/a><\/strong> is a change in a single nucleotide in DNA. This type of mutation is usually less serious than a chromosomal alteration. An example of a point mutation is a mutation that changes the codon UUU to the codon UCU. Point mutations can be silent, missense, or nonsense mutations, as described in Table 5.8.1. The effects of point mutations depend on how they change the genetic code.<\/p>\n<table style=\"height: 101px;width: 100%\">\n<caption>Table 5.8.1: The Effects of Point Mutations<\/caption>\n<thead>\n<tr style=\"height: 14px\">\n<th scope=\"col\">Type<\/th>\n<th scope=\"col\">Description<\/th>\n<th scope=\"col\">Example<\/th>\n<th scope=\"col\">Effect<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr style=\"height: 29px\">\n<td>Silent<\/td>\n<td>mutated codon codes for the same <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2279\">amino\u00a0acid<\/a><\/td>\n<td>CAA (glutamine) \u2192 CAG (glutamine)<\/td>\n<td>none<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td>Missense<\/td>\n<td>mutated codon codes for a different amino\u00a0acid<\/td>\n<td>CAA (glutamine) \u2192 CCA (proline)<\/td>\n<td>variable<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td>Nonsense<\/td>\n<td>mutated codon is a premature stop codon<\/td>\n<td>CAA (glutamine) \u2192 UAA (stop) usually<\/td>\n<td>serious<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>Frameshift Mutations<\/h2>\n<p>A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2689\">frameshift mutation<\/a><\/strong>\u00a0is a deletion or insertion of one or more nucleotides, changing the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2080\">reading frame<\/a> of the\u00a0base\u00a0sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in\u00a0RNA:<\/p>\n<p><strong>AUG-AAU-ACG-GCU = start-asparagine-threonine-alanine<\/strong><\/p>\n<p>Now, assume that an insertion occurs in this sequence. Let\u2019s say an\u00a0<strong>A <\/strong>nucleotide is inserted after the start codon\u00a0<strong>AUG.<\/strong>\u00a0The sequence of bases becomes:<\/p>\n<p><strong>AUG-AA<span style=\"color: #800000;background-color: #ffff99\">A<\/span>-UAC-GGC-U = start-lysine-tyrosine-glycine<\/strong><\/p>\n<p>Even though the rest of the sequence is unchanged, this insertion changes the reading frame and, therefore, all of the codons that follow it. As this example shows, a frameshift mutation can dramatically change how the codons in mRNA are read. This can have a drastic effect on the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2422\">protein<\/a>\u00a0product.<\/p>\n<div>\n<h1>Effects of Mutations<\/h1>\n<\/div>\n<p>The majority of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2381\">mutations<\/a>\u00a0have neither negative nor positive effects on the organism in which they occur. These mutations are called neutral mutations. Examples include silent point mutations, which are neutral because they do not change the\u00a0amino acids\u00a0in the\u00a0proteins\u00a0they encode.<\/p>\n<p>Many other mutations have no effects on the organism because they are repaired before\u00a0protein synthesis\u00a0occurs.\u00a0Cells\u00a0have multiple repair mechanisms to fix mutations in DNA.<\/p>\n<h2>Beneficial Mutations<\/h2>\n<p>Some mutations \u2014 known as\u00a0<strong>beneficial mutations<\/strong>\u00a0\u2014\u00a0have a positive effect on the organism in which they occur. They generally code for new versions of\u00a0proteins\u00a0that help organisms adapt to their environment. If they increase an organism\u2019s chances of surviving or reproducing, the mutations are likely to become more common over time. There are several well-known examples of beneficial mutations. Here are two such examples:<\/p>\n<ol>\n<li>Mutations have occurred in\u00a0bacteria\u00a0that allow the bacteria to survive in the presence of antibiotic drugs, leading to the evolution of antibiotic-resistant strains of bacteria.<\/li>\n<li>A unique mutation is found in people in <a href=\"https:\/\/en.wikipedia.org\/wiki\/Limone_sul_Garda\">Limone<\/a>,\u00a0 a small town in Italy. The mutation protects them from developing atherosclerosis, which is the dangerous buildup of fatty materials in blood vessels despite a high-fat diet. The individual in which this mutation first appeared has even been identified and many of his descendants carry this gene.<\/li>\n<\/ol>\n<h2>Harmful Mutations<\/h2>\n<p>Imagine making a random change in a complicated\u00a0machine, such as a car engine.\u00a0There is a chance that the random change would result in a car that does not run well \u2014 or perhaps does not run at all. By the same token, a random change in a gene's DNA may result in the production of a\u00a0protein\u00a0that does not function normally... or may not function at all.\u00a0Such mutations are likely to be harmful.\u00a0<strong>Harmful mutations<\/strong>\u00a0may cause\u00a0genetic disorders\u00a0or\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2148\">cancer<\/a>.<\/p>\n<ul>\n<li>A <strong>genetic disorder<\/strong> is a disease, syndrome, or other abnormal condition caused by a mutation in one or more genes, or by a chromosomal alteration. An example of a genetic disorder is <a href=\"https:\/\/en.wikipedia.org\/wiki\/Cystic_fibrosis\">cystic fibrosis<\/a>. A mutation in a single gene causes the body to produce thick, sticky mucus that clogs the lungs and blocks ducts in digestive organs.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2148\">Cancer<\/a> <\/strong>is a disease in which\u00a0cells\u00a0grow out of control and form abnormal masses of cells (called tumors). It is generally caused by mutations in genes that regulate the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2196\">cell cycle<\/a>. Because of the mutations, cells with damaged <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_277\">DNA<\/a> are allowed to divide without restriction.<\/li>\n<\/ul>\n<div>\n<h1>Feature: My\u00a0Human Body<\/h1>\n<\/div>\n<p>Inherited mutations are thought to play a role in roughly five to ten per cent of all cancers. Specific mutations that cause many of the known hereditary cancers have been identified. Most of the mutations occur in genes that control the growth of cells or the repair of damaged DNA.<\/p>\n<p>Genetic testing can be done to determine whether individuals have inherited specific cancer-causing mutations. Some of the most common inherited cancers for which genetic testing is available include hereditary <a href=\"https:\/\/en.wikipedia.org\/wiki\/Breast_cancer\">breast<\/a> and <a href=\"https:\/\/en.wikipedia.org\/wiki\/Ovarian_cancer\">ovarian\u00a0cancer<\/a>, caused by mutations in genes\u00a0called\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/BRCA_mutation\">BRCA1 and BRCA2<\/a>. Besides breast and ovarian cancers, mutations in these genes may also cause pancreatic and prostate cancers.\u00a0Genetic testing is generally done on a small sample of body fluid or tissue, such as\u00a0blood, saliva, or skin cells. The sample is analyzed by a lab that specializes in genetic testing, and it usually takes at least a few weeks to get the test results.<\/p>\n<p>Should you get genetic testing to find out whether you have inherited a cancer-causing mutation? Such testing is not done routinely just to screen patients for risk of cancer. Instead, the tests are generally done only when the following three criteria are met:<\/p>\n<ol>\n<li>The test can determine definitively whether a specific gene mutation is present. This is the case with the BRCA1 and BRCA2 gene mutations, for example.<\/li>\n<li>The test results would be useful to help guide future medical care. For example, if you found out you had a mutation in the BRCA1 or BRCA2 gene, you might get more frequent breast and ovarian cancer screenings than are generally recommended.<\/li>\n<li>You have a personal or family history that suggests you are at risk of an inherited cancer.<\/li>\n<\/ol>\n<p>Criterion number 3 is based, in turn, on such factors as:<\/p>\n<ul>\n<li>Diagnosis of cancer at an unusually young age.<\/li>\n<li>Several different cancers occurring independently in the same individual.<\/li>\n<li>Several close genetic relatives having the same type of cancer (such as a maternal grandmother, mother, and sister all having breast cancer).<\/li>\n<li>Cancer occurring in both organs in a set of paired organs (such as both kidneys or both breasts).<\/li>\n<\/ul>\n<p>If you meet the criteria for genetic testing and are advised to undergo it, genetic counseling is highly recommended. A genetic counselor can help you understand what the results mean and how to make use of them to reduce your risk of developing cancer. For example, a positive test result that shows the presence of a mutation may not\u00a0<em>necessarily<\/em>\u00a0mean that you will develop cancer. It may depend on whether the gene is located on an autosome or sex chromosome, and whether the mutation is dominant or recessive. Lifestyle factors may also play a role in cancer risk even for hereditary cancers. Early detection can often be life saving if cancer does develop. Genetic counseling can also help you assess the chances that any children you may have will inherit the mutation.<\/p>\n<div>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.8 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2381\">Mutations<\/a> are random changes in the sequence of bases in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_277\">DNA<\/a> or\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_519\">RNA<\/a>. Most people have multiple mutations in their DNA without ill effects. Mutations are the ultimate source of all new\u00a0genetic variation\u00a0in any\u00a0species.<\/li>\n<li>Mutations may happen spontaneously during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2086\">DNA replication<\/a> or\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2241\">transcription<\/a>. Other mutations are caused by environmental factors called mutagens. Mutagens include radiation, certain chemicals, and some infectious agents.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2106\">Germline mutations<\/a> occur in gametes and may be passed onto offspring. Every cell in the offspring will then have the mutation. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2192\">Somatic mutations<\/a> occur in cells other than gametes and are confined to just one cell and its daughter cells. These mutations cannot be passed on to offspring.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2388\">Chromosomal alterations<\/a> are mutations that change chromosome structure and usually affect the organism in multiple ways.\u00a0Charcot-Marie-Tooth disease type 1\u00a0is an example of a chromosomal alteration in humans.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2389\">Point mutations<\/a> are changes in a single nucleotide. The effects of point mutations depend on how they change the\u00a0genetic code\u00a0and may range from no effects to very serious effects.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2392\">Frameshift mutations<\/a> change the reading frame of the\u00a0genetic code\u00a0and are likely to have a drastic effect on the encoded\u00a0protein.<\/li>\n<li>Many mutations are neutral and have no effect on the organism in which they occur. Some mutations are beneficial and improve fitness. An example is a mutation that confers antibiotic\u00a0resistance\u00a0in\u00a0bacteria. Other mutations are harmful and decrease fitness, such as the mutations that cause\u00a0genetic disorders\u00a0or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2148\">cancers<\/a>.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.8 Review Question<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>Define mutation.<\/li>\n<li>Identify causes of mutation.<\/li>\n<li>Compare and contrast germline and somatic mutations.<\/li>\n<li>Describe chromosomal alterations, point mutations, and frameshift mutations. Identify the potential effects of each type of mutation.<\/li>\n<li>Why\u00a0do many mutations have neutral effects?<\/li>\n<li>Give one\u00a0example of a beneficial mutation and one\u00a0example of a harmful mutation.<\/li>\n<li>\n<div id=\"h5p-68\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-68\" class=\"h5p-iframe\" data-content-id=\"68\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Mutations\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<li>Why do you think that exposure to mutagens (such as cigarette smoke) can cause cancer?<\/li>\n<li>Explain why the insertion or deletion of a single nucleotide can cause a frameshift mutation.<\/li>\n<li>Compare and contrast missense and nonsense mutations.<\/li>\n<li>Explain why mutations are important to\u00a0evolution.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.8 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>https:\/\/www.youtube.com\/watch?time_continue=51&amp;v=PQjL4ZDuq2o&amp;feature=emb_logo<\/p>\n<p style=\"text-align: center\">How Radiation Changes Your DNA, Seeker, 2016.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=z9HIYjRRaDE&amp;t=93s<\/p>\n<p style=\"text-align: center\">Where do genes come from? - Carl Zimmer, TED-Ed, 2014.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=a63t8r70QN0&amp;feature=youtu.be<\/p>\n<p style=\"text-align: center\">What you should know about vaping and e-cigarettes | Suchitra Krishnan-Sarin,<br \/>\nTED, 2019.<\/p>\n<\/div>\n<\/div>\n<h2>Attributions<\/h2>\n<p><strong>Figure 5.8.1<\/strong><\/p>\n<p><a href=\"https:\/\/www.flickr.com\/photos\/patloika\/11027734365\/in\/photostream\/\" rel=\"cc:attributionURL\">Ninja Turtles<\/a>\u00a0by\u00a0<a href=\"https:\/\/www.flickr.com\/photos\/patloika\/\" rel=\"dc:creator\">Pat Loika<\/a> on <a href=\"https:\/\/www.flickr.com\/\">Flickr<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.0\/\">CC BY 2.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by\/2.0\/<a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\" rel=\"license\">)<\/a> license.<\/p>\n<p><strong>Figure 5.8.2<\/strong><\/p>\n<div>Examples of Mutagens by Christine MIller is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\">CC BY SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) license.<br \/>\nSeparate images are all in public domain or CC licensed:<\/div>\n<ul>\n<li><a style=\"font-size: 1em\" href=\"https:\/\/pixabay.com\/illustrations\/beauty-treatment-face-mask-girl-163540\/\">Beauty treatment face mask<\/a><span style=\"font-size: 1em\"> by <\/span><a style=\"font-size: 1em\" href=\"https:\/\/pixabay.com\/users\/no-longer-here-19203\/\">no-longer-here<\/a><span style=\"font-size: 1em\"> on <\/span><a style=\"font-size: 1em\" href=\"https:\/\/pixabay.com\/\">Pixabay<\/a><span style=\"font-size: 1em\"> is used under the <\/span><a style=\"font-size: 1em\" href=\"https:\/\/pixabay.com\/service\/license\/\">Pixabay License<\/a><span style=\"font-size: 1em\"> (https:\/\/pixabay.com\/service\/license\/).<\/span><\/li>\n<li><a href=\"https:\/\/www.flickr.com\/photos\/ajc1\/277161177\">HPV<\/a> by <a class=\"owner-name truncate\" title=\"Go to AJC1's photostream\" href=\"https:\/\/www.flickr.com\/photos\/ajc1\/\" data-track=\"attributionNameClick\">AJC1<\/a> on <a href=\"https:\/\/www.flickr.com\/\">Flickr<\/a> is used under a\u00a0<a href=\"https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/\">CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.<\/li>\n<li><span style=\"background-color: #ffffff\"><a style=\"background-color: #ffffff\" href=\"https:\/\/www.flickr.com\/search\/?user_id=47353092%40N00&amp;view_all=1&amp;text=bacteria\">H Pylori<\/a> by <a class=\"owner-name truncate\" style=\"background-color: #ffffff\" title=\"Go to AJC1's photostream\" href=\"https:\/\/www.flickr.com\/photos\/ajc1\/\" data-track=\"attributionNameClick\">AJC1<\/a> on <a style=\"background-color: #ffffff\" href=\"https:\/\/www.flickr.com\/\">Flickr<\/a> is used under a <a style=\"background-color: #ffffff\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/\">CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\u00a0<\/span><\/li>\n<li><span style=\"font-size: 1em\"><a href=\"https:\/\/www.flickr.com\/photos\/vaping360\/18539459466\">Vape and Cigarette<\/a> by <a class=\"owner-name truncate\" title=\"Go to Vaping360's photostream\" href=\"https:\/\/www.flickr.com\/photos\/vaping360\/\" data-track=\"attributionNameClick\">Vaping360<\/a><\/span> on <a href=\"https:\/\/www.flickr.com\/\">Flickr<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.0\/\">CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/li>\n<li><span style=\"font-size: 1em\"><a href=\"https:\/\/commons.wikimedia.org\/w\/index.php?curid=12143891\">Hand X-Ray<\/a> by<\/span> <a title=\"User:Hellerhoff\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Hellerhoff\">Hellerhoff<\/a> on Wikimedia Commons - <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/deed.en\">CC BY-SA 3.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/deed.en) license.<\/li>\n<li><a href=\"https:\/\/www.pxfuel.com\/en\/free-photo-obmsy\"><span style=\"font-size: 1em\">Hot dogs<\/span><\/a><span style=\"font-size: 1em\"> by unknown on <a href=\"https:\/\/www.pxfuel.com\/\">PxFuel<\/a> is used under the <a href=\"https:\/\/www.pxfuel.com\/terms-of-use\">Pxfuel Terms <\/a>(https:\/\/www.pxfuel.com\/terms-of-use).<\/span><\/li>\n<li>Sunshine face is clipart.<\/li>\n<\/ul>\n<p><strong>Figure 5.8.3<\/strong><\/p>\n<p><span style=\"text-align: initial;font-size: 1em;color: #373d3f\">Scheme of possible chromosome mutations\/ <a href=\"https:\/\/commons.wikimedia.org\/w\/index.php?curid=1413589\">Chromosomenmutationen<\/a> by unknown on Wikimedia Commons is adapted from N<\/span><span style=\"color: #373d3f;font-size: 1em\">IH<\/span><span style=\"text-align: initial;font-size: 1em;color: #373d3f\">'s <a href=\"https:\/\/www.genome.gov\/genetics-glossary\/Mutation\">Talking Glossary of Genetics<\/a>. [Changes as described by <a href=\"https:\/\/de.wikipedia.org\/wiki\/Benutzer:Dietzel65\">de:user:Dietzel65<\/a>]. Further use and adapation (text translated to English) by\u00a0<\/span><span style=\"text-align: initial;font-size: 1em;color: #373d3f\">Christine Miller as image is in the <a style=\"text-align: initial;font-size: 1em\" href=\"https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/\" rel=\"license\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/span><\/p>\n<p>&nbsp;<\/p>\n<p><span style=\"font-size: 1.424em;font-weight: bold\">References<\/span><\/p>\n<p class=\"hanging-indent\">Seeker. (2016, April 23). How radiation changes your DNA. YouTube. https:\/\/www.youtube.com\/watch?v=PQjL4ZDuq2o&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">TED. (2019, June 5). What you should know about vaping and e-cigarettes | Suchitra Krishnan-Sarin. YouTube. https:\/\/www.youtube.com\/watch?v=a63t8r70QN0&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">TED-Ed. (2014, September 22). Where do genes come from? - Carl Zimmer. YouTube. https:\/\/www.youtube.com\/watch?v=z9HIYjRRaDE&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, July 6). Breast cancer. In Wikipedia.\u00a0 https:\/\/en.wikipedia.org\/w\/index.php?title=Breast_cancer&amp;oldid=966366739<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, July 9). Charcot\u2013Marie\u2013Tooth disease. In <em>Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Charcot%E2%80%93Marie%E2%80%93Tooth_disease&amp;oldid=966912915<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, July 7). Cystic fibrosis. In <em>Wikipedia<\/em>.\u00a0 https:\/\/en.wikipedia.org\/w\/index.php?title=Cystic_fibrosis&amp;oldid=966566921<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, June 4). Limone sul Garda. In\u00a0<i>Wikipedia. <\/i>https:\/\/en.wikipedia.org\/w\/index.php?title=Limone_sul_Garda&amp;oldid=960771991<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, June 23). Ovarian cancer. In <em>Wikipedia<\/em>.\u00a0 https:\/\/en.wikipedia.org\/w\/index.php?title=Ovarian_cancer&amp;oldid=964157192<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, May 7). BRCA mutation. In <em>Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=BRCA_mutation&amp;oldid=955463902<\/p>\n<p class=\"hanging-indent\">Wikipedia contributors. (2020, July 10). Teenage Mutant Ninja Turtles. In <em>Wikipedia<\/em>. https:\/\/en.wikipedia.org\/w\/index.php?title=Teenage_Mutant_Ninja_Turtles&amp;oldid=967030468<\/p>\n<p>&nbsp;<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_5857\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_5857\"><div tabindex=\"-1\"><p>Body cavity that fills the lower half of the trunk and holds the kidneys and the digestive and reproductive organs.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_5975\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_5975\"><div tabindex=\"-1\"><p>A major human body cavity that includes the head and the posterior (back) of the trunk and holds the brain and spinal cord.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_5961\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_5961\"><div tabindex=\"-1\"><p>A cavity that fills most of the upper part of the skull and contains the brain.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_2928\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_2928\"><div tabindex=\"-1\"><p>Created by: CK-12\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_384\" aria-describedby=\"caption-attachment-384\" style=\"width: 844px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-2461\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/kelly-sikkema-FqqaJI9OxMI-unsplash-scaled-1.jpg\" alt=\"Image shows a dark, curly-haired man in his 20s or 30s holding and kissing a toddler with similar physical features and curly, dark hair, while the toddler smiles. \" width=\"844\" height=\"625\"><figcaption id=\"caption-attachment-384\" class=\"wp-caption-text\"><em>Figure 5.11.1 Like Father, Like Son.<\/em><\/figcaption><\/figure>\n<h1>Like Father, Like Son<\/h1>\n<p>This father-son duo share some similarities.\u00a0 The shape of their faces and their facial features look very similar. If you saw them together, you might well guess that they are father and son. People have long known that the characteristics of living things are similar between parents and their offspring. However, it wasn\u2019t until the experiments of Gregor Mendel\u00a0that scientists understood\u00a0<em>how<\/em>\u00a0those traits are inherited.<\/p>\n<div>\n<h1>The Father of Genetics<\/h1>\n<\/div>\n<p>Mendel did experiments with pea plants to show how traits such as seed shape and flower colour are inherited. Based on his research, he developed his two well known laws of inheritance: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2445\">law of segregation<\/a> and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2447\">law of independent assortment<\/a>. When Mendel died in 1884, his work was still virtually unknown. In 1900, three other researchers working independently came to the same conclusions that Mendel had drawn almost half a century earlier. Only then was Mendel's work rediscovered.<\/p>\n<p>Mendel knew nothing about genes, because they\u00a0were discovered after his death. He did think, however, that some type of \"factors\" controlled traits, and that those \"factors\" were passed from parents to offspring. We now call these \"factors\" genes.\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2462\">Mendel's laws\u00a0of inheritance<\/a>, now expressed in terms of genes,\u00a0form the basis of\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2712\">genetics<\/a><\/strong>, the science of heredity. For this reason, Mendel is often called the father of genetics.<\/p>\n<div>\n<h1>The Language of Genetics<\/h1>\n<\/div>\n<p>Today, we know that traits of organisms are controlled by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2035\">genes<\/a> on\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2166\">chromosomes<\/a>. To talk about inheritance in terms of genes and chromosomes, you need to know the language of genetics.\u00a0The terms below serve\u00a0as\u00a0a good starting point. They are illustrated in the\u00a0figure\u00a0that follows.<\/p>\n<ul>\n<li>A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2035\">gene<\/a><\/strong> is the part of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2166\">chromosome<\/a> that contains the\u00a0genetic code\u00a0for a given\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2422\">protein<\/a>. For example, in\u00a0pea plants, a given gene might code for flower\u00a0colour.<\/li>\n<li>The position of a given gene on a chromosome is called its\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2465\">locus<\/a> <\/strong>(plural, loci). A gene might be located near the center, or at one end or the other of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2166\">chromosome<\/a>.<\/li>\n<li>A given gene may have different normal versions, which are called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_1942\">alleles<\/a><\/strong><strong>.<\/strong> For example, in\u00a0pea plants, there is a purple-flower allele (B) and a white-flower allele (b) for the flower-colour\u00a0gene. Different\u00a0alleles account for much of the variation in the traits of organisms, including people.<\/li>\n<li>In sexually reproducing organisms, each individual has two copies of each type of chromosome. Paired\u00a0chromosomes\u00a0of the same type are called\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2153\"><strong>homologous<\/strong><strong>\u00a0<\/strong><strong>chromosomes<\/strong><\/a>. They are about the same size and shape, and they have all the same genes at the same loci.<\/li>\n<\/ul>\n<figure id=\"attachment_384\" aria-describedby=\"caption-attachment-384\" style=\"width: 500px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-383 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/f-d_56cb7ecdd193e58369e5f34a1b55594b30afa8c99312e8001ee5b70bIMAGE_THUMB_POSTCARD_TINYIMAGE_THUMB_POSTCARD_TINY.png\" alt=\"\" width=\"500\" height=\"203\"><figcaption id=\"caption-attachment-384\" class=\"wp-caption-text\"><em>Figure 5.11.2 Chromosome, Gene, Locus, and Allele. This diagram shows how the concepts of chromosome, gene, locus, and allele are related. What is the difference between a gene and a locus? Between a gene and an allele?<\/em><\/figcaption><\/figure>\n<div>\n<h2>Genotype<\/h2>\n<\/div>\n<p>When\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2468\">sexual reproduction<\/a>\u00a0occurs, sex\u00a0cells\u00a0(called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2694\">gametes<\/a>) unite during\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2677\">fertilization<\/a>\u00a0to form a single cell called a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2471\">zygote<\/a><\/strong>. The zygote inherits two of each type of chromosome, with one chromosome of each type coming from the father, and the other coming from the mother. Because <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2153\">homologous chromosomes<\/a> have the same genes at the same loci, each individual also inherits two copies of each gene. The two copies may be the same allele or different\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_1942\">alleles<\/a>. The alleles an individual inherits for a given gene make up the individual\u2019s\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2715\">genotype<\/a><\/strong>. \u00a0As shown in Table 5.11.1, an organism with two of the same allele (for example, <em>BB<\/em>\u00a0or\u00a0<em>bb<\/em>) is called a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2473\">homozygote<\/a><\/strong>. An organism with two different alleles (in this example,\u00a0<em>Bb<\/em>) is called a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2474\">heterozygote<\/a><\/strong>.<\/p>\n<p><strong>Table 5.11.1\u00a0<\/strong><\/p>\n<p><em>Allele Combinations Associated With the Terms Homozygous and Heterozygous<\/em><\/p>\n<p><img class=\"wp-image-384 \" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Untitled.png\" alt=\"Illustrates allele combinations associated with the terms homozygous and heterozygous\" width=\"746\" height=\"345\"><\/p>\n<p>&nbsp;<\/p>\n<p><span style=\"font-size: 1.424em;font-weight: bold\">Phenotype<\/span><\/p>\n<p>The expression of an organism\u2019s genotype is referred to as its\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2477\">phenotype<\/a><\/strong>, and it refers to the organism\u2019s traits, such as purple or white flowers in pea plants. As you can see from Table 5.11.1, different genotypes may produce the same phenotype. In this example, both <em>BB<\/em>\u00a0and\u00a0<em>Bb<\/em>\u00a0genotypes produce plants with the same phenotype, purple flowers. Why does this happen? In a\u00a0<em>Bb<\/em>\u00a0heterozygote, only the\u00a0<em>B<\/em>\u00a0allele is expressed, so the\u00a0<em>b <\/em>allele doesn\u2019t influence the phenotype. In general, when only one of two alleles is expressed in the phenotype, the expressed allele is called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2630\">dominant<\/a>,<\/strong>\u00a0and the allele that isn\u2019t expressed is called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2479\">recessive<\/a>.<\/strong><\/p>\n<p>The terms\u00a0<em>dominant<\/em>\u00a0and\u00a0<em>recessive<\/em> may also be used to refer to phenotypic traits. For example, purple flower colour in pea plants is a dominant trait. It shows up in the phenotype whenever a plant inherits even one dominant allele for the trait. Similarly, white flower colour is a recessive trait. Like other recessive traits, it shows up in the phenotype only when a plant inherits <em>two<\/em>\u00a0recessive alleles for the trait.<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.11 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>Mendel's laws\u00a0of inheritance, now expressed in terms of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2035\">genes<\/a>, form the basis of genetics, which is the science of heredity.\u00a0This is why Mendel is often called the father of genetics.<\/li>\n<li>A gene is the part of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2166\">chromosome<\/a> that codes for a given\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2422\">protein<\/a>. The position of a gene on a chromosome is its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2465\">locus<\/a>.\u00a0\u00a0A given gene may have different versions, called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_1942\">alleles<\/a>.\u00a0Paired chromosomes of the same type are called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2153\">homologous chromosomes<\/a>. They have the same size and shape, and they have the same genes at the same <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2465\">loci<\/a>.<\/li>\n<li>The alleles an individual inherits for a given gene make up the individual's <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2715\">genotype<\/a>. An organism with two of the same allele is called a homozygote, and an individual with two different alleles is called a heterozygote.<\/li>\n<li>The expression of an organism's genotype is referred to as its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2477\">phenotype<\/a>. A dominant allele is always expressed in the phenotype, even when just one dominant allele has been inherited. A recessive allele is expressed in the phenotype only when two recessive alleles have been inherited.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.11 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>Define genetics.<\/li>\n<li>Why is Gregor Mendel called the father of genetics if genes were not discovered until after his death?<\/li>\n<li>\n<div id=\"h5p-71\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-71\" class=\"h5p-iframe\" data-content-id=\"71\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Genetic of Inheritance\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<li>Imagine that there are two alleles, <em>R <\/em>and\u00a0<em>r<\/em>, for a given gene.\u00a0<em>R<\/em>\u00a0is dominant to\u00a0<em>r<\/em>. Answer the following questions about this gene:\n<ol type=\"a\">\n<li>What are the possible homozygous and heterozygous genotypes?<\/li>\n<li>Which genotype or genotypes express the dominant\u00a0<em>R\u00a0<\/em>phenotype? Explain your answer.<\/li>\n<li>Are <em>R <\/em>and\u00a0<em>r<\/em>\u00a0on different loci? Why or why not?<\/li>\n<li>Can <em>R <\/em>and\u00a0<em>r<\/em>\u00a0be on the same exact chromosome? Why or why not? If not, where are they located?<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.11 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>https:\/\/www.youtube.com\/watch?v=pv3Kj0UjiLE<\/p>\n<p style=\"text-align: center\">Alleles and Genes, Amoeba Sisters, 2018.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=OaovnS7BAoc<\/p>\n<p style=\"text-align: center\">Genotypes and Phenotypes, Bozeman Science, 2011.<\/p>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<h2>Attributions<\/h2>\n<p><strong>Figure 5.11.1<\/strong><\/p>\n<p><a href=\"https:\/\/unsplash.com\/photos\/FqqaJI9OxMI\">Father holding his baby boy with matching haircut<\/a> [photo] by <a href=\"https:\/\/unsplash.com\/@kellysikkema\">Kelly Sikkema<\/a> on <a href=\"http:\/\/Unsplash.com\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\n<p><strong>Figure 5.11.2<\/strong><\/p>\n<p><a href=\"https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.10\/\">Chromosome, Gene, Locus, and Allele<\/a>\u00a0by <a href=\"https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/5.10\/\">CK-12 Foundation<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/\">CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.<\/p>\n<p><img src=\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/logo_ck12.png\" alt=\"\"> <span style=\"font-size: 1em\">\u00a9<\/span><a style=\"font-size: 1em\" href=\"http:\/\/www.ck12.org\/\">CK-12 Foundation<\/a> <span style=\"font-size: 1em\">Licensed under\u00a0<\/span><a style=\"font-size: 1em\" href=\"http:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/\"><img class=\"alignnone size-full wp-image-8217\" title=\"CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0)\" src=\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/icon_licence.png\" alt=\"CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0)\"><\/a><span style=\"font-size: 1em\">\u00a0\u2022\u00a0<\/span><a style=\"font-size: 1em\" href=\"http:\/\/www.ck12.org\/about\/terms-of-use\/\">Terms of Use<\/a><span style=\"font-size: 1em\">\u00a0\u2022\u00a0<\/span><a style=\"font-size: 1em\" href=\"http:\/\/www.ck12.org\/about\/attribution\/\">Attribution<\/a><\/p>\n<p><strong>Table 5.11.1<\/strong><\/p>\n<p><em>Allele Combinations Associated With the Terms Homozygous and Heterozygous<\/em> by Christine Miller is released into the <a style=\"text-align: initial;font-size: 1em\" href=\"https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/\" rel=\"license\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/p>\n<h2>References<\/h2>\n<p class=\"hanging-indent\">Amoeba Sisters. (2018, February 1). Alleles and genes. YouTube. https:\/\/www.youtube.com\/watch?v=pv3Kj0UjiLE&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Bozeman Science. (2011, August 4). Genotypes and phenotypes. YouTube. https:\/\/www.youtube.com\/watch?v=OaovnS7BAoc&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Brainard, J\/ CK-12 Foundation. (2016). Figure 2 Chromosome, gene, locus, and allele [digital image]. In <em>CK-12 College Human Biology\u00a0<\/em>(Section 5.10) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-human-biology\/section\/5.9\/<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_2929\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_2929\"><div tabindex=\"-1\"><p>Created by: CK-12\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_394\" aria-describedby=\"caption-attachment-394\" style=\"width: 496px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-2482\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/loly-galina-JrHhKeQBM9A-unsplash-scaled-1.jpg\" alt=\"Image demonstrates that within a family, the offspring resemble their parents, but are slightly different from both the parents and their siblings.\" width=\"496\" height=\"744\"><figcaption id=\"caption-attachment-394\" class=\"wp-caption-text\"><em>Figure 5.12.1 Family resemblance. <\/em><\/figcaption><\/figure>\n<h1>All in the Family<\/h1>\n<p>This family photo (Figure 5.12.1) clearly illustrates an important point: children in a family resemble their parents and each other, but the children never look exactly the same, unless they are identical twins. Each of the daughters in the photo have inherited a unique combination of traits from the parents. In this concept, you will learn how this happens. It all begins with sex \u2014 sexual reproduction, that is.<\/p>\n<div>\n<h1>Sexual Reproduction<\/h1>\n<\/div>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2414\">Reproduction<\/a><\/strong>\u00a0is the process by which organisms give rise to offspring. It is one of the defining characteristics of living things. Like many other organisms, human beings reproduce sexually.\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2468\">Sexual reproduction<\/a> <\/strong>involves two parents. As you can see from Figure 5.12.2, in sexual reproduction, parents produce reproductive (sex) cells \u2014 called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2694\">gametes<\/a>\u00a0<\/strong>\u2014 that unite to form an offspring. Gametes are\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2484\">haploid<\/a><\/strong>\u00a0(or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2485\">1N<\/a>)\u00a0cells.\u00a0This means they contain one copy of each chromosome in the\u00a0nucleus.\u00a0Gametes are produced by a type of\u00a0cell division\u00a0called\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2486\">meiosis<\/a>, which is described in detail below. The process in which two gametes unite is called\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2677\"><strong>fertilizat<\/strong><strong>i<\/strong><strong>on<\/strong><\/a>. The fertilized cell that results is referred to as a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2471\">zygote<\/a><\/strong>. A zygote is a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2103\">diploid<\/a><\/strong>\u00a0(or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2103\">2N<\/a>) cell,\u00a0which means it contains two copies of each chromosome. Thus, it has twice the number of\u00a0chromosomes\u00a0as a gamete.<\/p>\n<figure id=\"attachment_394\" aria-describedby=\"caption-attachment-394\" style=\"width: 555px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-388\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Human-Life-Cycle.png\" alt=\"Image illustrates the human life cycle\" width=\"555\" height=\"464\"><figcaption id=\"caption-attachment-394\" class=\"wp-caption-text\"><em>Figure 5.12.2 Sexual reproduction involves the production of haploid gametes by meiosis, followed by fertilization and the formation of a diploid zygote. The number of chromosomes in a gamete is represented by the letter N. Why does the zygote have 2N, or twice as many, chromosomes?<\/em><\/figcaption><\/figure>\n<div>\n<h1>Meiosis<\/h1>\n<\/div>\n<p>The process that produces haploid gametes is called meiosis.\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2486\">Meiosis<\/a><\/strong> is a type of cell division in which the number of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2166\">chromosomes<\/a> is reduced by half. It occurs only in certain special cells of an organism. During meiosis, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2153\">homologous (paired) chromosomes<\/a> separate, and four <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2484\">haploid<\/a> cells form that have only one chromosome from each pair. The diagram (Figure 5.12.3) gives an overview of meiosis.<\/p>\n<figure id=\"attachment_394\" aria-describedby=\"caption-attachment-394\" style=\"width: 587px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-389\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/MajorEventsInMeiosis_variant_int.png\" alt=\"Image shows the major events in Meiosis\" width=\"587\" height=\"352\"><figcaption id=\"caption-attachment-394\" class=\"wp-caption-text\"><em>Figure 5.12.3 Overview of Meiosis. During meiosis, homologous chromosomes separate and go to different daughter cells. This diagram shows just the nuclei of the cells. Notice the exchange of genetic material that occurs prior to the first cell division.<\/em><\/figcaption><\/figure>\n<div>\n<p>&nbsp;<\/p>\n<\/div>\n<p>As you can see in\u00a0the meiosis diagram, two cell divisions occur during the overall process,\u00a0producing\u00a0a total of four <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2484\">haploid<\/a> cells from one parent cell. The two cell divisions are called meiosis I and meiosis II.\u00a0Meiosis I begins after\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2086\">DNA\u00a0replicates<\/a> during interphase. Meiosis II follows meiosis I without DNA replicating again. Both meiosis I and meiosis II occur in four phases, called prophase, metaphase, anaphase, and telophase. You may recognize these four phases from\u00a0mitosis, the division of the\u00a0nucleus\u00a0that takes place during routine\u00a0cell division\u00a0of eukaryotic cells.<\/p>\n<h2>Meiosis I- Increasing genetic variation<\/h2>\n<p>The phases of Meiosis I are:<\/p>\n<ol>\n<li><strong>Prophase I:<\/strong>\u00a0The nuclear envelope begins to break down, and the\u00a0chromosomes\u00a0condense. Centrioles start moving to opposite poles of the cell, and a spindle begins to form. Importantly, homologous chromosomes pair up, which is unique to prophase I. In prophase of\u00a0mitosis\u00a0and meiosis II, homologous chromosomes do not form pairs in this way. During prophase I, crossing-over occurs. The significance of crossing-over is discussed below.<\/li>\n<li><strong>Metaphase I:<\/strong> Spindle fibres attach to the paired homologous chromosomes. The paired chromosomes line up along the equator of the cell, randomly aligning in a process called independent alignment.\u00a0 The significance of independent alignment is discussed below. This occurs only in metaphase I. In metaphase of mitosis and meiosis II, it is sister chromatids that line up along the equator of the cell.<\/li>\n<li><strong>Anaphase I:<\/strong> Spindle fibres shorten, and the chromosomes of each homologous pair start to separate from each other. One chromosome of each pair moves toward one pole of the cell, and the other chromosome moves toward the opposite pole.<\/li>\n<li><strong>Telophase I and Cytokinesis:<\/strong>\u00a0The spindle breaks down, and new nuclear membranes form. The cytoplasm of the cell divides, and two haploid daughter cells result. The daughter cells each have a random assortment of chromosomes, with one from each homologous pair. Both daughter cells go on to meiosis II.<\/li>\n<\/ol>\n<figure id=\"attachment_394\" aria-describedby=\"caption-attachment-394\" style=\"width: 1052px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-390 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Meiosis-1.png\" alt=\"Illustrates the stages in Meiosis I\" width=\"1052\" height=\"582\"><figcaption id=\"caption-attachment-394\" class=\"wp-caption-text\"><em>Figure 5.12.4 Meiosis I is critical in creating genetic diversity in resulting gametes. Crossing over, in Prophase I and independent alignment in Metaphase I ensure that each resulting gamete is unique.<\/em><\/figcaption><\/figure>\n<h2>Meiosis II- Halfing the DNA<\/h2>\n<p>The phases of Meiosis II are:<\/p>\n<ol>\n<li><strong>Prophase II:<\/strong>\u00a0The nuclear envelope breaks down, and the spindle begins to form in each haploid daughter cell from meiosis I. The centrioles also start to separate.<\/li>\n<li><strong>Metaphase II:<\/strong> Spindle fibres line up the sister chromatids of each chromosome along the equator of the cell.<\/li>\n<li><strong>Anaphase II:<\/strong>\u00a0Sister chromatids separate and move to opposite poles.<\/li>\n<li><strong>Telophase II and Cytokinesis:<\/strong>\u00a0The spindle breaks down, and new nuclear membranes form. The cytoplasm of each cell divides, and four haploid cells result. Each cell has a unique combination of chromosomes.<\/li>\n<\/ol>\n<div>\n<div>\n<figure id=\"attachment_391\" aria-describedby=\"caption-attachment-391\" style=\"width: 1000px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-391 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Meiosis-2-1.png\" alt=\"Image shows the stages of Meiosis II\" width=\"1000\" height=\"582\"><figcaption id=\"caption-attachment-391\" class=\"wp-caption-text\"><em>Figure 5.12.5 In Meiosis II, dyads are separated to create four unique haploid cells.<\/em><\/figcaption><\/figure>\n<h1>Sexual Reproduction and\u00a0Genetic Variation<\/h1>\n<\/div>\n<p>\"It takes two to tango\" might be a euphemism for sexual reproduction. Requiring\u00a0<em>two<\/em>\u00a0individuals to produce offspring, however, is also the main drawback of this way of reproducing, because it requires extra steps \u2014 and often a certain amount of luck \u2014 to successfully reproduce with a partner. On the other hand, sexual reproduction greatly increases the potential for\u00a0genetic variation\u00a0in offspring,\u00a0which\u00a0increases the likelihood that the resulting offspring will have genetic advantages. In fact, each offspring produced is almost guaranteed to be genetically unique, differing from both parents and from any other offspring. Sexual reproduction increases genetic variation in a number of ways:<\/p>\n<figure id=\"attachment_393\" aria-describedby=\"caption-attachment-393\" style=\"width: 518px\" class=\"wp-caption alignright\"><img class=\"wp-image-392\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Corssing-Over-by-OpenStax.jpg\" alt=\"Image shows the process of crossing over as it occurs in Meiosis I\" width=\"518\" height=\"363\"><figcaption id=\"caption-attachment-393\" class=\"wp-caption-text\"><em>Figure 5.12.6 Crossing over results in exchange of sections of DNA between homologous pairs of chromosomes.<\/em><\/figcaption><\/figure>\n<ul>\n<li>When homologous chromosomes pair up during meiosis I, crossing-over can occur.\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2500\">Crossing-over<\/a> <\/strong>is the exchange of genetic material between non-sister chromatids of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2153\">homologous chromosomes<\/a>. It results in new combinations of genes on each chromosome. This is called recombination. You can see how it happens in the figure to the right.<\/li>\n<li>When cells divide during meiosis, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of each other. This is called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2502\">independent alignment<\/a><\/strong>. It results in gametes that have unique combinations of chromosomes.\u00a0 You can see how it happens in Figure 5.12.7.<\/li>\n<li>In sexual reproduction, two gametes unite to produce an offspring. But which two of the millions of possible gametes will it be? This is a matter of chance, and it's obviously another source of genetic variation in offspring.<\/li>\n<\/ul>\n<figure id=\"attachment_393\" aria-describedby=\"caption-attachment-393\" style=\"width: 512px\" class=\"wp-caption alignleft\"><img class=\"wp-image-393 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Independent_assortment.svg_.png\" alt=\"Image shows how independent alignment increases genetic diversity in gametes.\" width=\"512\" height=\"217\"><figcaption id=\"caption-attachment-393\" class=\"wp-caption-text\"><em>Figure 5.12.7 Independent alignment greatly increases the genetic diversity among gametes produced.\u00a0 Depending on how the homologous pairs align (with paternal or maternal DNA on the left or right side) determines which mix of genes will end up in each of the four unique haploid gametes produced.<\/em><\/figcaption><\/figure>\n<p>With all of this recombination of genes, there is a need for a new set of vocabulary.\u00a0 Remember, that sister chromatids are two\u00a0<em>identical<\/em> pieces of DNA connected at a centromere.\u00a0 Once crossing over has occured, we can no longer call them sister chromatids since they are no longer identical; we term them <strong>dyads.\u00a0 <\/strong>In addition, once crossing over has occurred, the pair of homologous chromosomes can be referred to as\u00a0<strong>tetrads.\u00a0\u00a0<\/strong><\/p>\n<p>All of these mechanisms\u00a0\u2014\u00a0crossing over, independent assortment, and the random union of gametes\u00a0\u2014\u00a0work together to result in an amazing\u00a0range\u00a0of potential genetic variation. Each human couple, for example, has the potential to produce more than 64 trillion genetically unique children. No wonder we are all different!<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=VzDMG7ke69g<\/p>\n<p style=\"text-align: center\">Meiosis (updated), Amoeba Sisters, 2017.<\/p>\n<h1>Gametogenesis<\/h1>\n<\/div>\n<p>At the end of meiosis, four haploid cells have been produced, but the cells are not yet gametes. The cells need to develop before they become mature gametes capable of\u00a0fertilization. The\u00a0development\u00a0of haploid cells into gametes is called\u00a0<strong>gametogenesis<\/strong>. It\u00a0differs between males and females.<\/p>\n<ul>\n<li>A gamete produced by a male is called a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2506\">sperm<\/a><\/strong><strong>,<\/strong>\u00a0and the process that produces a mature\u00a0sperm\u00a0is\u00a0called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2507\">spermatogenesis<\/a><\/strong>. During this process, a sperm cell grows a tail and gains the ability to \u201cswim,\u201d like the human sperm cell shown in Figure 5.12.8.<\/li>\n<li>A gamete produced by a female is called an<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2467\"><strong>egg or ovum,<\/strong><\/a>\u00a0and the process that produces a mature egg is called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2509\">oogenesis<\/a><\/strong>, during which just one functional egg is produced. The other three haploid cells that result from meiosis are called polar bodies, and they disintegrate. The single egg is a very large cell, as you can see from the human egg also shown in Figure 5.12.8.<\/li>\n<\/ul>\n<figure id=\"attachment_394\" aria-describedby=\"caption-attachment-394\" style=\"width: 391px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-394 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Fertilization.jpg\" alt=\"Image shows a sperm fertilizing an egg.\" width=\"391\" height=\"265\"><figcaption id=\"caption-attachment-394\" class=\"wp-caption-text\"><em>Figure 5.12.8 A human sperm is a tiny cell with a tail. A human egg is much larger. Both cells are mature haploid gametes that are capable of fertilization. What process is shown in this photograph?<\/em><\/figcaption><\/figure>\n<div>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.12 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>In <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2468\">sexual reproduction<\/a>, two parents produce <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2694\">gametes<\/a> that unite in the process of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2677\">fertilization<\/a>\u00a0to form a single-celled <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2471\">zygote<\/a>. Gametes are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2484\">haploid<\/a> cells with one copy of each of the 23 chromosomes, and the zygote is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2103\">diploid<\/a> cell with two\u00a0copies of each of the 23 chromosomes.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2486\">Meiosis<\/a> is the type of cell division that produces four haploid daughter cells that may become gametes. Meiosis occurs in two stages, called meiosis I and meiosis II, each of which occurs in four phases (prophase, metaphase, anaphase, and telophase).<\/li>\n<li>Meiosis is followed by\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2697\">gametogenesis<\/a>, the process during which the haploid daughter cells change into mature gametes. Males produce gametes called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2506\">sperm<\/a> in a process known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2507\">spermatogenesis<\/a>, and females produce gametes called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2467\">eggs<\/a> in the process known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2509\">oogenesis<\/a>.<\/li>\n<li>Sexual reproduction produces genetically unique offspring. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2500\">Crossing-over<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4724_2502\">independent alignment<\/a>, and the random union of gametes work together to result in an amazing range of potential genetic variation.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.12 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>\n<div id=\"h5p-72\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-72\" class=\"h5p-iframe\" data-content-id=\"72\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Sexual Reproduction, Meiosis and Gametogenesis\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<li>Explain how sexual reproduction happens\u00a0at the cellular level.<\/li>\n<li>Summarize what happens during Meiosis.<\/li>\n<li>Compare and contrast gametogenesis in males and females.<\/li>\n<li>Explain the mechanisms that increase genetic variation in the offspring produced by sexual reproduction.<\/li>\n<li>Why do gametes need to be haploid? What would happen to the chromosome number after fertilization if they were diploid?<\/li>\n<li>Describe one difference between Prophase I of Meiosis and Prophase of Mitosis.<\/li>\n<li>Do all of the chromosomes that you got from your mother go into one of your gametes? Why or why not?<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">5.12 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>https:\/\/www.youtube.com\/watch?v=qCLmR9-YY7o&amp;feature=emb_logo<\/p>\n<p style=\"text-align: center\">Meiosis: Where the Sex Starts - Crash Course Biology #13, CrashCourse, 2012.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=zrKdz93WlVk<\/p>\n<p style=\"text-align: center\">Mitosis vs Meiosis Comparison, Amoeba Sisters, 2018.<\/p>\n<\/div>\n<\/div>\n<p><span style=\"font-size: 1.424em;font-weight: bold\">Attributions<\/span><\/p>\n<\/div>\n<p><strong>Figure 5.12.1<\/strong><\/p>\n<p><a href=\"https:\/\/unsplash.com\/photos\/JrHhKeQBM9A\" rel=\"cc:attributionURL\">Family portrait<\/a> by <a class=\"_3XzpS _1ByhS _4kjHg _1O9Y0 _3l__V _1CBrG xLon9\" href=\"https:\/\/unsplash.com\/@lolygalina\">loly galina<\/a> on <a href=\"https:\/\/unsplash.com\/\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\n<p><strong>Figure 5.12.2<\/strong><\/p>\n<p>Human Life Cycle by Christine Miller is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\" rel=\"license\">CC BY-NC-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.<\/p>\n<p><strong>Figure 5.12.3<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:MajorEventsInMeiosis_variant_int.svg\" rel=\"cc:attributionURL\">MajorEventsInMeiosis_variant_int<\/a> by <a title=\"User:Patr\u00edciaR\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Patr%C3%ADciaR\">Patr\u00edciaR<\/a><span style=\"text-align: initial;font-size: 1em\">\u00a0(i<span style=\"font-size: 1em\">nternationalization) on Wikimedia Commons is used and <\/span>adapted by Christine Miller. This image<\/span><span style=\"text-align: initial;font-size: 1em\">\u00a0in the <\/span><a class=\"extiw\" style=\"text-align: initial;font-size: 1em\" title=\"w:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/public_domain\">public domain.<\/a> (<span style=\"text-align: initial;font-size: 1em\">Original image from <a href=\"https:\/\/en.wikipedia.org\/wiki\/National_Center_for_Biotechnology_Information\">NCBI<\/a>; original vector version by <a title=\"User:Jakov\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Jakov\">Jakov.<\/a>)<\/span><\/p>\n<p><strong>Figure 5.12.4<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Meiosis_Stages.svg\" rel=\"cc:attributionURL\">Meiosis 1\/ Meiosis Stages<\/a> by <span style=\"color: #0000ff\"><a class=\"mw-redirect\" style=\"color: #0000ff\" title=\"User:Ali Zifan\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Ali_Zifan\">Ali Zifan<\/a><\/span> on Wikimedia Commons is used and adapted by Christine Miller under a\u00a0 <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en\">CC <span style=\"font-size: 1em\">BY-SA 4.0<\/span><\/a><span style=\"text-align: initial;font-size: 1em\">\u00a0 (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.<\/span><\/p>\n<p><strong>Figure 5.12.5<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Meiosis_Stages.svg\" rel=\"cc:attributionURL\">Meiosis 2\/ Meiosis Stages <\/a> by <span style=\"color: #0000ff\"><a class=\"mw-redirect\" style=\"color: #0000ff\" title=\"User:Ali Zifan\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Ali_Zifan\">Ali Zifan<\/a><\/span> on Wikimedia Commons is used and adapted by Christine Miller under a\u00a0 <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en\">CC <span style=\"font-size: 1em\">BY-SA 4.0<\/span><\/a><span style=\"text-align: initial;font-size: 1em\">\u00a0 (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.<\/span><\/p>\n<p><strong>Figure 5.12.6<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Figure_17_02_01.jpg\" rel=\"cc:attributionURL\">Crossover\/ Figure 17 02 01<\/a> by <a href=\"https:\/\/cnx.org\/contents\/GFy_h8cu@10.53:Qq6Y1A16@5\/Mapping-Genomes\">CNX OpenStax<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.<\/p>\n<p><strong>Figure 5.12.7<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Independent_assortment.svg\" rel=\"cc:attributionURL\">Independent_assortment<\/a> by <a class=\"new\" title=\"User:Mtian20 (page does not exist)\" href=\"https:\/\/commons.wikimedia.org\/w\/index.php?title=User:Mtian20&amp;action=edit&amp;redlink=1\">Mtian20<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\" rel=\"license\">CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.<\/p>\n<p><strong>Figure 5.12.8<\/strong><\/p>\n<p><a href=\"https:\/\/www.flickr.com\/photos\/81461206@N02\/7468551760\/\">sperm fertilizing egg<\/a> by <a class=\"owner-name truncate\" title=\"Go to AndreaLaurel's photostream\" href=\"https:\/\/www.flickr.com\/photos\/81461206@N02\/\" data-track=\"attributionNameClick\">AndreaLaurel<\/a> on <a href=\"http:\/\/flickr.com\">Flickr<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.0\/\">CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/) license.<\/p>\n<h2>References<\/h2>\n<p class=\"hanging-indent\">Amoeba Sisters. (2017, July 11). Meiosis (updated). YouTube. https:\/\/www.youtube.com\/watch?v=VzDMG7ke69g&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Amoeba Sisters. (2018, May 31). Mitosis vs meiosis comparison. YouTube. https:\/\/www.youtube.com\/watch?v=zrKdz93WlVk&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">CrashCourse, (2012, April 23). Meiosis: Where the sex starts - Crash Course Biology #13. YouTube. https:\/\/www.youtube.com\/watch?v=qCLmR9-YY7o&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">OpenStax CNX. (2016, May 27). Figure 1 Crossover may occur at different locations on the chromosome<span style=\"text-align: initial;font-size: 1em\">. <\/span><span style=\"text-align: initial;font-size: 1em\">In <\/span><em style=\"text-align: initial;font-size: 1em\">OpenStax, Biology <\/em>(Section 17.2)<span style=\"text-align: initial;font-size: 1em\">. http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.53.<\/span><\/p>\n<p class=\"hanging-indent\">\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4724_5939\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4724_5939\"><div tabindex=\"-1\"><p>Clear fluid produced by the brain that forms a thin layer within the meninges and provides protection and cushioning for the brain and spinal cord.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":32,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":"cc-by-nc"},"chapter-type":[48],"contributor":[],"license":[55],"class_list":["post-4724","chapter","type-chapter","status-publish","hentry","chapter-type-numberless","license-cc-by-nc"],"part":4681,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4724","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/users\/32"}],"version-history":[{"count":4,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4724\/revisions"}],"predecessor-version":[{"id":6430,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4724\/revisions\/6430"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/parts\/4681"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4724\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/media?parent=4724"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapter-type?post=4724"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/contributor?post=4724"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/license?post=4724"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}