{"id":2764,"date":"2016-06-13T17:29:02","date_gmt":"2016-06-13T17:29:02","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/biologyxwaymakerxmaster\/?post_type=chapter&#038;p=2764"},"modified":"2024-04-29T16:33:50","modified_gmt":"2024-04-29T16:33:50","slug":"reading-pleiotropy-lethal-alleles-and-sex-linkage","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/reading-pleiotropy-lethal-alleles-and-sex-linkage\/","title":{"raw":"Pleiotropy and Human Disorders","rendered":"Pleiotropy and Human Disorders"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Explain pleiotropy and its impact on traits in a population<\/li>\r\n<\/ul>\r\n<\/div>\r\nBased on Mendel\u2019s experiments, you might imagine that all genes control a single characteristic, are present in two copies, and affect some harmless aspect of an organism\u2019s appearance (such as color, height, or shape). Although those predictions are accurate in many cases, there are also some important exceptions. For instance, how can we explain observations like the following?\r\n<ul>\r\n \t<li>The genetic disorder Marfan syndrome is caused by a mutation in one gene, yet it affects many aspects of growth and development, including height, vision, and heart function.<\/li>\r\n<\/ul>\r\nTo understand observations like these, we need to look more deeply at what genes are. Rather than abstract \u201cheritable factors,\u201d genes are stretches of DNA found on chromosomes, and most of them encode (specify the sequence of) proteins that do a certain job in the cell or body. In this article, we\u2019ll look in more detail at genes affecting multiple characteristics (pleiotropy).\r\n<h2>Pleiotropy<\/h2>\r\nWhen we discussed Mendel\u2019s experiments with purple-flowered and white-flowered plants, we didn\u2019t mention any other phenotypes associated with the two flower colors. However, Mendel noticed that the flower colors were always correlated with two other features: the color of the seed coat (covering of the seed) and the color of the axils (junctions where the leaves met the main stem)[footnote]Lobo, I. (2008). Pleiotropy: One gene can affect multiple traits. <em>Nature Education<\/em>, <em>1<\/em>(1), 10. Retrieved from <a href=\"http:\/\/www.nature.com\/scitable\/topicpage\/pleiotropy-one-gene-can-affect-multiple-traits-569\" target=\"_blank\" rel=\"noopener\">www.nature.com\/scitable\/topicpage\/pleiotropy-one-gene-can-affect-multiple-traits-569<\/a>.[\/footnote]. In plants with white flowers, the seed coats and axils were colorless, while in plants with purple flowers, the seed coats were brown-gray and the axils were reddish. Thus, rather than affecting just one characteristic, the flower color gene actually affected three.\r\n\r\n[caption id=\"attachment_2940\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-2940\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/06\/15210254\/pleiotropy.png\" alt=\" Simple schematic illustrating pleiotropy. In pleiotropy, one gene affects multiple features (feature 1, feature 2, feature 3. Caption: One gene affects multiple characteristics.\" width=\"400\" height=\"290\" \/> Based on similar diagram by Ingrid Lobo[\/caption]\r\n\r\nGenes like this, which affect multiple, seemingly unrelated aspects of an organism\u2019s phenotype, are said to be <strong>pleiotropic<\/strong> (<em>pleio<\/em>- = many, -<em>tropic<\/em> = effects)[footnote]<em>Ibid<\/em>.[\/footnote]. We now know that Mendel\u2019s flower color gene encodes a regulator protein that activates pigment biosynthesis, and that it works in several different parts of the pea plant (flowers, seed coat, and leaf axils). Thus, the seemingly unrelated phenotypes can all be traced back to a defect in a single gene with several jobs.\r\n\r\nAlleles of pleiotropic genes are transmitted in the same way as alleles of genes that affect single traits. In these cases, the difference is that the phenotype contains multiple elements. These elements are specified as a package, and there would be both a dominant and recessive version of this package of traits.\r\n<h2>Pleiotropy in Human Genetic Disorders<\/h2>\r\nGenes affected in human genetic disorders are often pleiotropic. For example, people with the hereditary disorder Marfan syndrome may have a constellation of seemingly unrelated symptoms[footnote]Marfan syndrome. (2012). In <em>Genetics home reference<\/em>. Retrieved from\u00a0<a href=\"http:\/\/ghr.nlm.nih.gov\/condition\/marfan-syndrome\" target=\"_blank\" rel=\"noopener\">http:\/\/ghr.nlm.nih.gov\/condition\/marfan-syndrome<\/a>.[\/footnote]:\r\n<ul>\r\n \t<li>Unusually tall height<\/li>\r\n \t<li>Thin fingers and toes<\/li>\r\n \t<li>Dislocation of the lens of the eye<\/li>\r\n \t<li>Heart problems (in which the aorta, the large blood vessel carrying blood away from the heart, bulges or ruptures).<\/li>\r\n<\/ul>\r\nThese symptoms don\u2019t appear directly related to one another, but as it turns out, they can all be traced back to the mutation of a single gene. This gene encodes a protein that assembles into chains, making elastic fibrils that give strength and flexibility to the body\u2019s connective tissues[footnote]FBN1. (2015). In <em>Genetics home reference<\/em>. Retrieved from <a href=\"http:\/\/ghr.nlm.nih.gov\/gene\/FBN1\" target=\"_blank\" rel=\"noopener\">http:\/\/ghr.nlm.nih.gov\/gene\/FBN1<\/a>.[\/footnote]. Disease-causing mutations in the Marfan syndrome reduce the amount of functional protein produced, resulting in fewer fibrils. The eye and the aorta normally contain many fibrils that help maintain structure, explaining why these two organs are strongly affected in Marfan syndrome[footnote]Marfan syndrome. (2015, November 3). Retrieved November 21, 2015 from Wikipedia: <a href=\"https:\/\/en.wikipedia.org\/wiki\/Marfan_syndrome\" target=\"_blank\" rel=\"noopener\">https:\/\/en.wikipedia.org\/wiki\/Marfan_syndrome<\/a>.[\/footnote]. In addition, the fibrils serve as \u201cstorage shelves\u201d for growth factors. When there are fewer of them in Marfan syndrome, the growth factors cannot be shelved and thus cause excess growth (leading to the characteristic tall, thin Marfan build)[footnote]FBN1. (2015). In <em>Genetics home reference<\/em>. Retrieved from <a href=\"http:\/\/ghr.nlm.nih.gov\/gene\/FBN1\" target=\"_blank\" rel=\"noopener\">http:\/\/ghr.nlm.nih.gov\/gene\/FBN1<\/a>.[\/footnote].\r\n\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/3d9aea19-f98b-4d01-bf26-e211b9f56bfe\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Explain pleiotropy and its impact on traits in a population<\/li>\n<\/ul>\n<\/div>\n<p>Based on Mendel\u2019s experiments, you might imagine that all genes control a single characteristic, are present in two copies, and affect some harmless aspect of an organism\u2019s appearance (such as color, height, or shape). Although those predictions are accurate in many cases, there are also some important exceptions. For instance, how can we explain observations like the following?<\/p>\n<ul>\n<li>The genetic disorder Marfan syndrome is caused by a mutation in one gene, yet it affects many aspects of growth and development, including height, vision, and heart function.<\/li>\n<\/ul>\n<p>To understand observations like these, we need to look more deeply at what genes are. Rather than abstract \u201cheritable factors,\u201d genes are stretches of DNA found on chromosomes, and most of them encode (specify the sequence of) proteins that do a certain job in the cell or body. In this article, we\u2019ll look in more detail at genes affecting multiple characteristics (pleiotropy).<\/p>\n<h2>Pleiotropy<\/h2>\n<p>When we discussed Mendel\u2019s experiments with purple-flowered and white-flowered plants, we didn\u2019t mention any other phenotypes associated with the two flower colors. However, Mendel noticed that the flower colors were always correlated with two other features: the color of the seed coat (covering of the seed) and the color of the axils (junctions where the leaves met the main stem)<a class=\"footnote\" title=\"Lobo, I. (2008). Pleiotropy: One gene can affect multiple traits. Nature Education, 1(1), 10. Retrieved from www.nature.com\/scitable\/topicpage\/pleiotropy-one-gene-can-affect-multiple-traits-569.\" id=\"return-footnote-2764-1\" href=\"#footnote-2764-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a>. In plants with white flowers, the seed coats and axils were colorless, while in plants with purple flowers, the seed coats were brown-gray and the axils were reddish. Thus, rather than affecting just one characteristic, the flower color gene actually affected three.<\/p>\n<div id=\"attachment_2940\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2940\" class=\"wp-image-2940\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/06\/15210254\/pleiotropy.png\" alt=\"Simple schematic illustrating pleiotropy. In pleiotropy, one gene affects multiple features (feature 1, feature 2, feature 3. Caption: One gene affects multiple characteristics.\" width=\"400\" height=\"290\" \/><\/p>\n<p id=\"caption-attachment-2940\" class=\"wp-caption-text\">Based on similar diagram by Ingrid Lobo<\/p>\n<\/div>\n<p>Genes like this, which affect multiple, seemingly unrelated aspects of an organism\u2019s phenotype, are said to be <strong>pleiotropic<\/strong> (<em>pleio<\/em>&#8211; = many, &#8211;<em>tropic<\/em> = effects)<a class=\"footnote\" title=\"Ibid.\" id=\"return-footnote-2764-2\" href=\"#footnote-2764-2\" aria-label=\"Footnote 2\"><sup class=\"footnote\">[2]<\/sup><\/a>. We now know that Mendel\u2019s flower color gene encodes a regulator protein that activates pigment biosynthesis, and that it works in several different parts of the pea plant (flowers, seed coat, and leaf axils). Thus, the seemingly unrelated phenotypes can all be traced back to a defect in a single gene with several jobs.<\/p>\n<p>Alleles of pleiotropic genes are transmitted in the same way as alleles of genes that affect single traits. In these cases, the difference is that the phenotype contains multiple elements. These elements are specified as a package, and there would be both a dominant and recessive version of this package of traits.<\/p>\n<h2>Pleiotropy in Human Genetic Disorders<\/h2>\n<p>Genes affected in human genetic disorders are often pleiotropic. For example, people with the hereditary disorder Marfan syndrome may have a constellation of seemingly unrelated symptoms<a class=\"footnote\" title=\"Marfan syndrome. (2012). In Genetics home reference. Retrieved from\u00a0http:\/\/ghr.nlm.nih.gov\/condition\/marfan-syndrome.\" id=\"return-footnote-2764-3\" href=\"#footnote-2764-3\" aria-label=\"Footnote 3\"><sup class=\"footnote\">[3]<\/sup><\/a>:<\/p>\n<ul>\n<li>Unusually tall height<\/li>\n<li>Thin fingers and toes<\/li>\n<li>Dislocation of the lens of the eye<\/li>\n<li>Heart problems (in which the aorta, the large blood vessel carrying blood away from the heart, bulges or ruptures).<\/li>\n<\/ul>\n<p>These symptoms don\u2019t appear directly related to one another, but as it turns out, they can all be traced back to the mutation of a single gene. This gene encodes a protein that assembles into chains, making elastic fibrils that give strength and flexibility to the body\u2019s connective tissues<a class=\"footnote\" title=\"FBN1. (2015). In Genetics home reference. Retrieved from http:\/\/ghr.nlm.nih.gov\/gene\/FBN1.\" id=\"return-footnote-2764-4\" href=\"#footnote-2764-4\" aria-label=\"Footnote 4\"><sup class=\"footnote\">[4]<\/sup><\/a>. Disease-causing mutations in the Marfan syndrome reduce the amount of functional protein produced, resulting in fewer fibrils. The eye and the aorta normally contain many fibrils that help maintain structure, explaining why these two organs are strongly affected in Marfan syndrome<a class=\"footnote\" title=\"Marfan syndrome. (2015, November 3). Retrieved November 21, 2015 from Wikipedia: https:\/\/en.wikipedia.org\/wiki\/Marfan_syndrome.\" id=\"return-footnote-2764-5\" href=\"#footnote-2764-5\" aria-label=\"Footnote 5\"><sup class=\"footnote\">[5]<\/sup><\/a>. In addition, the fibrils serve as \u201cstorage shelves\u201d for growth factors. When there are fewer of them in Marfan syndrome, the growth factors cannot be shelved and thus cause excess growth (leading to the characteristic tall, thin Marfan build)<a class=\"footnote\" title=\"FBN1. (2015). In Genetics home reference. Retrieved from http:\/\/ghr.nlm.nih.gov\/gene\/FBN1.\" id=\"return-footnote-2764-6\" href=\"#footnote-2764-6\" aria-label=\"Footnote 6\"><sup class=\"footnote\">[6]<\/sup><\/a>.<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_3d9aea19-f98b-4d01-bf26-e211b9f56bfe\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/3d9aea19-f98b-4d01-bf26-e211b9f56bfe?iframe_resize_id=assessment_practice_id_3d9aea19-f98b-4d01-bf26-e211b9f56bfe\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-2764\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Pleiotropy, lethal alleles, and sex linkage. <strong>Provided by<\/strong>: Khan Academy. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/www.khanacademy.org\/science\/biology\/classical-genetics\/variations-on-mendelian-genetics\/a\/pleiotropy-lethal-alleles-and-sex-linkage\">https:\/\/www.khanacademy.org\/science\/biology\/classical-genetics\/variations-on-mendelian-genetics\/a\/pleiotropy-lethal-alleles-and-sex-linkage<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section><hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-2764-1\">Lobo, I. (2008). Pleiotropy: One gene can affect multiple traits. <em>Nature Education<\/em>, <em>1<\/em>(1), 10. Retrieved from <a href=\"http:\/\/www.nature.com\/scitable\/topicpage\/pleiotropy-one-gene-can-affect-multiple-traits-569\" target=\"_blank\" rel=\"noopener\">www.nature.com\/scitable\/topicpage\/pleiotropy-one-gene-can-affect-multiple-traits-569<\/a>. <a href=\"#return-footnote-2764-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><li id=\"footnote-2764-2\"><em>Ibid<\/em>. <a href=\"#return-footnote-2764-2\" class=\"return-footnote\" aria-label=\"Return to footnote 2\">&crarr;<\/a><\/li><li id=\"footnote-2764-3\">Marfan syndrome. (2012). In <em>Genetics home reference<\/em>. Retrieved from\u00a0<a href=\"http:\/\/ghr.nlm.nih.gov\/condition\/marfan-syndrome\" target=\"_blank\" rel=\"noopener\">http:\/\/ghr.nlm.nih.gov\/condition\/marfan-syndrome<\/a>. <a href=\"#return-footnote-2764-3\" class=\"return-footnote\" aria-label=\"Return to footnote 3\">&crarr;<\/a><\/li><li id=\"footnote-2764-4\">FBN1. (2015). In <em>Genetics home reference<\/em>. Retrieved from <a href=\"http:\/\/ghr.nlm.nih.gov\/gene\/FBN1\" target=\"_blank\" rel=\"noopener\">http:\/\/ghr.nlm.nih.gov\/gene\/FBN1<\/a>. <a href=\"#return-footnote-2764-4\" class=\"return-footnote\" aria-label=\"Return to footnote 4\">&crarr;<\/a><\/li><li id=\"footnote-2764-5\">Marfan syndrome. (2015, November 3). Retrieved November 21, 2015 from Wikipedia: <a href=\"https:\/\/en.wikipedia.org\/wiki\/Marfan_syndrome\" target=\"_blank\" rel=\"noopener\">https:\/\/en.wikipedia.org\/wiki\/Marfan_syndrome<\/a>. <a href=\"#return-footnote-2764-5\" class=\"return-footnote\" aria-label=\"Return to footnote 5\">&crarr;<\/a><\/li><li id=\"footnote-2764-6\">FBN1. (2015). In <em>Genetics home reference<\/em>. Retrieved from <a href=\"http:\/\/ghr.nlm.nih.gov\/gene\/FBN1\" target=\"_blank\" rel=\"noopener\">http:\/\/ghr.nlm.nih.gov\/gene\/FBN1<\/a>. <a href=\"#return-footnote-2764-6\" class=\"return-footnote\" aria-label=\"Return to footnote 6\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":20,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Pleiotropy, lethal alleles, and sex linkage\",\"author\":\"\",\"organization\":\"Khan Academy\",\"url\":\"https:\/\/www.khanacademy.org\/science\/biology\/classical-genetics\/variations-on-mendelian-genetics\/a\/pleiotropy-lethal-alleles-and-sex-linkage\",\"project\":\"\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"463c4e68-c448-49ab-8747-d1097eea46d4, c7706198-ea7f-4dfd-92f9-7bf21f141b38","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2764","chapter","type-chapter","status-publish","hentry"],"part":258,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2764","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":13,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2764\/revisions"}],"predecessor-version":[{"id":6017,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2764\/revisions\/6017"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/parts\/258"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2764\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/media?parent=2764"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapter-type?post=2764"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/contributor?post=2764"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/license?post=2764"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}