{"id":2761,"date":"2016-06-13T17:18:13","date_gmt":"2016-06-13T17:18:13","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/biologyxwaymakerxmaster\/?post_type=chapter&#038;p=2761"},"modified":"2023-09-05T21:48:00","modified_gmt":"2023-09-05T21:48:00","slug":"genetics-and-the-environment","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/chapter\/genetics-and-the-environment\/","title":{"raw":"Genetics and the Environment","rendered":"Genetics and the Environment"},"content":{"raw":"<h2>What you'll learn to do: Discuss the role environment plays on phenotypes<\/h2>\r\nIn recent years, scientists have begun to research how our\u00a0environment can impact our phenotypes: most common diseases are a result of both your genes and your environment. Your environment can include personal choices, such as what foods you eat and how much you exercise, and external factors, such as stress, clean water, and air quality. Most diseases, especially common diseases, are a combination of your genetic risk and your environment.\u00a0Only a small number of diseases are a result of just a single\u00a0mutation\u00a0in a\u00a0gene. Examples of these single-gene disorders are\u00a0Huntington disease<span class=\"ext\">\u00a0<\/span>and\u00a0Tay Sachs.\r\n\r\nIt is becoming difficult to group diseases into either purely \"genetic\" or \"environmental\" because most diseases are a little bit of both. For example, emphysema can be the result of both smoking and a\u00a0disorder\u00a0called\u00a0alpha-1-AT deficiency.\r\n\r\nIn this outcome, we'll learn about a few different ways our environment can impact us.\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe polygenic inheritance and how to recognize it<\/li>\r\n \t<li>Describe continuous variation and how to recognize it<\/li>\r\n \t<li>Explain pleiotropy and its impact on traits in a population<\/li>\r\n \t<li>Identify gene-environment interaction and how this impacts trait expression<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Polygenic Inheritance and Environmental Effects<\/h2>\r\n<h3>How is Height Inherited?<\/h3>\r\nMany heritable human characteristics don\u2019t seem to follow Mendelian rules in their inheritance patterns. For example, consider human height. Unlike a simple Mendelian characteristic, human height displays:\r\n<ul>\r\n \t<li><strong>Continuous variation.<\/strong> Unlike Mendel's pea plants, humans don\u2019t come in two clear-cut \u201ctall\u201d and \u201cshort\u201d varieties. In fact, they don't even come in four heights, or eight, or sixteen. Instead, it\u2019s possible to get humans of many different heights, and height can vary in increments of inches or fractions of inches. As an example, consider the bell curve-shaped graph in Figure 1, which shows the heights of a group of male high school seniors.<\/li>\r\n \t<li><strong>A complex inheritance pattern.<\/strong> If you've paid attention to the heights of your friends and family, you may have noticed that many different patterns of inheritance are possible. Tall parents can have a short child, short parents can have a tall child, and two parents of different heights may or may not have a child of intermediate height. In addition, siblings with the same two parents may have a range of heights, ones that don't fall into clear, distinct categories. Simple models involving one or two genes can't accurately predict all of these inheritance patterns.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_2932\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-2932\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/06\/15204204\/height-1024x631.png\" alt=\" Histogram showing height in inches of male high school seniors in a sample group. The histogram is roughly bell-shaped, with just a few individuals at the tails (60 inches and 77 inches) and many individuals in the middle, around 69 inches.\" width=\"400\" height=\"246\" \/> Figure 1. Heights of male high school seniors. Image modified from \"Continuous variation: Quantitative traits,\" by J. W. Kimball (CC BY 3.0).[\/caption]\r\n\r\nSome human characteristics, such as height, eye color, and hair color, don\u2019t come in just a few distinct forms. Instead, they vary in small gradations, forming a spectrum or continuum of possible phenotypes.\r\n\r\nHow, then, is height inherited? Height and other similar features are controlled not just by one gene, but rather, by multiple (often many) genes that each make a small contribution to the overall outcome. This inheritance pattern is called <strong>polygenic inheritance<\/strong> (<em>poly<\/em>- = many). For instance, a recent study found over 400 genes linked to variation in height[footnote]Wood, A. R., Esko, T., Yang, J., Vedantam, S., Pers, T. H., Gustafsson, S., ... Frayling, T. M. (2014). Defining the role of common variation in the genomic and biological architecture of adult human height. <em>Nature Genetics<\/em>, <em>46<\/em>, 1173\u20131186. <a href=\"http:\/\/dx.doi.org\/10.1038\/ng.3097\" target=\"_blank\" rel=\"noopener\">http:\/\/dx.doi.org\/10.1038\/ng.3097<\/a>.[\/footnote].\u00a0When there are large numbers of genes involved, it becomes hard to distinguish the effect of each individual gene, and even harder to see that gene variants (alleles) are inherited according to Mendelian rules. In a further complication, height doesn\u2019t just depend on genetics: it also depends a lot on environmental factors, such as a child\u2019s overall health and the type of nutrition he or she receives while growing up.\r\n<div class=\"textbox exercises\">\r\n<h3>PRactice Questions<\/h3>\r\nWe've learned about polygenic inheritance and continuous variation. Just what is the difference between these two types of inheritance?\r\n\r\n[practice-area rows=\"4\"][\/practice-area]\r\n[reveal-answer q=\"646463\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"646463\"]<em>Polygenic traits<\/em> are traits that rely on multiple genes. <em>Continuous variation<\/em> describes traits whose phenotypes occur on a continuum, rather than having a limited number of possible phenotypes. Traits with continuous variation are often also polygenic traits, but not always, and not all polygenic traits have continuous variation.[\/hidden-answer]\r\n\r\n<\/div>\r\n<h2>Pleiotropy and Human Disorders<\/h2>\r\n<h3>Pleiotropy<\/h3>\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)[\/footnote].\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\" \/> Figure 2. 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]. The seemingly unrelated phenotypes can all be traced back to a defect in a single gene with several jobs.\r\n\r\nImportantly, alleles of pleiotropic genes are transmitted in the same way as alleles of genes that affect single traits. Although the phenotype has multiple elements, these elements are specified as a package, and the dominant and recessive versions of the package would appear in the progeny of a monohybrid cross in a ratio of\u00a03:1.\r\n<h3>Pleiotropy in Human Genetic Disorders<\/h3>\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.\r\n<h2>Effect of the Environment<\/h2>\r\nCharacteristics that are influenced by environmental as well as genetic factors are called <strong>multifactorial<\/strong>. The idea of \u201cnature versus nurture\u201d \u2014 in other words, the relative influence of genetics versus environmental factors \u2014 has been and still is debated. Just looking at the genes of a given organism will not determine how that organism will develop and act. Even identical twins will show different characteristics, depending on the environment in which they live. Everyone is a product of their environment as well as their genetics.\r\n\r\n[caption id=\"attachment_2800\" align=\"alignright\" width=\"350\"]<img class=\"wp-image-2800\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/06\/13172732\/baby_foot.png\" alt=\"Blood from a newborn's foot is being placed on a card.\" width=\"350\" height=\"202\" \/> Figure 3. Taking a newborn blood sample for PKU testing. By Staff Sgt Eric T. Sheler, U.S. Air Force (Phenylketonuria testing) Public Domain[\/caption]\r\n\r\nEven when influenced by the environment, phenotypes have a normal range of expression. For instance, human height varies based on nutrition and genetics, but not many people are shorter than 4\u00bd feet or taller than 7 feet. The range of phenotypic possibilities is called the <em>norm of reaction<\/em>. Hydrangeas, for example, may be blue, pink, or purple, but they are never naturally orange. Hydrangeas are blue in acidic soil with available aluminum, and they are pink in alkaline soil without available aluminum.\r\n\r\nYou may have heard about PKU, a pleiotropic disorder caused by defects in a single gene coding for an enzyme that converts the amino acid phenylalanine to tyrosine. Newborns are tested for this defect very early in life (Figure 3), so that if the results are positive, they can be given a diet limiting phenylalanine ingestion. That way, the toxic buildup is prevented and the children can develop normally. PKU is an example in which environmental factors can modify gene expression.\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Question<\/h3>\r\nTwo identical twins (female) live in different parts of the country. One is very committed to a\u00a0healthy lifestyle: not smoking, exercising regularly, eating a diet rich in fresh produce, and avoiding red\u00a0meats and processed foods. The other is not as careful: she smokes, is overweight, and often eats fast\u00a0and processed foods. They are aware that several women in their family have had breast cancer, and\u00a0decide to consult a doctor about their odds of developing the disease. Which of the following statements\u00a0by the doctor sounds most correct?\r\n<ol>\r\n \t<li>As identical twins, you are genetically the same, so your chances of developing breast cancer are identical.<\/li>\r\n \t<li>The twin with the healthy lifestyle should not be terribly concerned, while the one with the unhealthy lifestyle is at a higher risk.<\/li>\r\n \t<li>Breast cancer has a genetic component, and the twins have identical genes, so they have the same genetic risk. However, environmental factors such as smoking, obesity, and consumption of red meat have been shown to increase the risk of cancer. While both twins should monitor themselves closely, the twin who smokes and is overweight may want to consider a healthier lifestyle to decrease her risk of breast cancer.<\/li>\r\n<\/ol>\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"41921\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"41921\"]Option A is wrong; while\u00a0it has been shown that certain genes may predispose people to cancer, there are many\u00a0associations between environmental effects and cancer. Option B is also wrong; familial cancers have a genetic component which may or may not be balanced by a healthy lifestyle. Option C is the most correct answer; lifestyle choices are important, but genetic influences are to be taken seriously, especially if\u00a0there is a family pattern associated with them.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox learning-objectives\">\r\n<h3>In Summary: Effect of the Environment<\/h3>\r\nWhile genes and genetic causes play a large role in health and phenotypes, the environment also plays an important role. Understanding this can enable the treatment of some disorders, such as the case with PKU in which limiting the intake of phenylalanine can prevent toxic build up of this amino acid. Often the norm of reaction is set by genetic factors but ultimately determined by environmental exposures.\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Check Your Understanding<\/h3>\r\nTraits with ________ will often display a bell curve-shaped distribution when graphed.\r\n<ul>\r\n \t<li>codominant inheritance<\/li>\r\n \t<li>continuous variation<\/li>\r\n \t<li>dominant-recessive inheritance<\/li>\r\n<\/ul>\r\n<details><summary>Show Answer<\/summary>continuous variation\r\n\r\n<\/details><\/div>","rendered":"<h2>What you&#8217;ll learn to do: Discuss the role environment plays on phenotypes<\/h2>\n<p>In recent years, scientists have begun to research how our\u00a0environment can impact our phenotypes: most common diseases are a result of both your genes and your environment. Your environment can include personal choices, such as what foods you eat and how much you exercise, and external factors, such as stress, clean water, and air quality. Most diseases, especially common diseases, are a combination of your genetic risk and your environment.\u00a0Only a small number of diseases are a result of just a single\u00a0mutation\u00a0in a\u00a0gene. Examples of these single-gene disorders are\u00a0Huntington disease<span class=\"ext\">\u00a0<\/span>and\u00a0Tay Sachs.<\/p>\n<p>It is becoming difficult to group diseases into either purely &#8220;genetic&#8221; or &#8220;environmental&#8221; because most diseases are a little bit of both. For example, emphysema can be the result of both smoking and a\u00a0disorder\u00a0called\u00a0alpha-1-AT deficiency.<\/p>\n<p>In this outcome, we&#8217;ll learn about a few different ways our environment can impact us.<\/p>\n<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe polygenic inheritance and how to recognize it<\/li>\n<li>Describe continuous variation and how to recognize it<\/li>\n<li>Explain pleiotropy and its impact on traits in a population<\/li>\n<li>Identify gene-environment interaction and how this impacts trait expression<\/li>\n<\/ul>\n<\/div>\n<h2>Polygenic Inheritance and Environmental Effects<\/h2>\n<h3>How is Height Inherited?<\/h3>\n<p>Many heritable human characteristics don\u2019t seem to follow Mendelian rules in their inheritance patterns. For example, consider human height. Unlike a simple Mendelian characteristic, human height displays:<\/p>\n<ul>\n<li><strong>Continuous variation.<\/strong> Unlike Mendel&#8217;s pea plants, humans don\u2019t come in two clear-cut \u201ctall\u201d and \u201cshort\u201d varieties. In fact, they don&#8217;t even come in four heights, or eight, or sixteen. Instead, it\u2019s possible to get humans of many different heights, and height can vary in increments of inches or fractions of inches. As an example, consider the bell curve-shaped graph in Figure 1, which shows the heights of a group of male high school seniors.<\/li>\n<li><strong>A complex inheritance pattern.<\/strong> If you&#8217;ve paid attention to the heights of your friends and family, you may have noticed that many different patterns of inheritance are possible. Tall parents can have a short child, short parents can have a tall child, and two parents of different heights may or may not have a child of intermediate height. In addition, siblings with the same two parents may have a range of heights, ones that don&#8217;t fall into clear, distinct categories. Simple models involving one or two genes can&#8217;t accurately predict all of these inheritance patterns.<\/li>\n<\/ul>\n<div id=\"attachment_2932\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2932\" class=\"wp-image-2932\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/06\/15204204\/height-1024x631.png\" alt=\"Histogram showing height in inches of male high school seniors in a sample group. The histogram is roughly bell-shaped, with just a few individuals at the tails (60 inches and 77 inches) and many individuals in the middle, around 69 inches.\" width=\"400\" height=\"246\" \/><\/p>\n<p id=\"caption-attachment-2932\" class=\"wp-caption-text\">Figure 1. Heights of male high school seniors. Image modified from &#8220;Continuous variation: Quantitative traits,&#8221; by J. W. Kimball (CC BY 3.0).<\/p>\n<\/div>\n<p>Some human characteristics, such as height, eye color, and hair color, don\u2019t come in just a few distinct forms. Instead, they vary in small gradations, forming a spectrum or continuum of possible phenotypes.<\/p>\n<p>How, then, is height inherited? Height and other similar features are controlled not just by one gene, but rather, by multiple (often many) genes that each make a small contribution to the overall outcome. This inheritance pattern is called <strong>polygenic inheritance<\/strong> (<em>poly<\/em>&#8211; = many). For instance, a recent study found over 400 genes linked to variation in height<a class=\"footnote\" title=\"Wood, A. R., Esko, T., Yang, J., Vedantam, S., Pers, T. H., Gustafsson, S., ... Frayling, T. M. (2014). Defining the role of common variation in the genomic and biological architecture of adult human height. Nature Genetics, 46, 1173\u20131186. http:\/\/dx.doi.org\/10.1038\/ng.3097.\" id=\"return-footnote-2761-1\" href=\"#footnote-2761-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a>.\u00a0When there are large numbers of genes involved, it becomes hard to distinguish the effect of each individual gene, and even harder to see that gene variants (alleles) are inherited according to Mendelian rules. In a further complication, height doesn\u2019t just depend on genetics: it also depends a lot on environmental factors, such as a child\u2019s overall health and the type of nutrition he or she receives while growing up.<\/p>\n<div class=\"textbox exercises\">\n<h3>PRactice Questions<\/h3>\n<p>We&#8217;ve learned about polygenic inheritance and continuous variation. Just what is the difference between these two types of inheritance?<\/p>\n<p><textarea aria-label=\"Your Answer\" rows=\"4\"><\/textarea><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q646463\">Show Answer<\/span><\/p>\n<div id=\"q646463\" class=\"hidden-answer\" style=\"display: none\"><em>Polygenic traits<\/em> are traits that rely on multiple genes. <em>Continuous variation<\/em> describes traits whose phenotypes occur on a continuum, rather than having a limited number of possible phenotypes. Traits with continuous variation are often also polygenic traits, but not always, and not all polygenic traits have continuous variation.<\/div>\n<\/div>\n<\/div>\n<h2>Pleiotropy and Human Disorders<\/h2>\n<h3>Pleiotropy<\/h3>\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)\" id=\"return-footnote-2761-2\" href=\"#footnote-2761-2\" aria-label=\"Footnote 2\"><sup class=\"footnote\">[2]<\/sup><\/a>.<\/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\">Figure 2. 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-2761-3\" href=\"#footnote-2761-3\" aria-label=\"Footnote 3\"><sup class=\"footnote\">[3]<\/sup><\/a>. The seemingly unrelated phenotypes can all be traced back to a defect in a single gene with several jobs.<\/p>\n<p>Importantly, alleles of pleiotropic genes are transmitted in the same way as alleles of genes that affect single traits. Although the phenotype has multiple elements, these elements are specified as a package, and the dominant and recessive versions of the package would appear in the progeny of a monohybrid cross in a ratio of\u00a03:1.<\/p>\n<h3>Pleiotropy in Human Genetic Disorders<\/h3>\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-2761-4\" href=\"#footnote-2761-4\" aria-label=\"Footnote 4\"><sup class=\"footnote\">[4]<\/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.<\/p>\n<h2>Effect of the Environment<\/h2>\n<p>Characteristics that are influenced by environmental as well as genetic factors are called <strong>multifactorial<\/strong>. The idea of \u201cnature versus nurture\u201d \u2014 in other words, the relative influence of genetics versus environmental factors \u2014 has been and still is debated. Just looking at the genes of a given organism will not determine how that organism will develop and act. Even identical twins will show different characteristics, depending on the environment in which they live. Everyone is a product of their environment as well as their genetics.<\/p>\n<div id=\"attachment_2800\" style=\"width: 360px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2800\" class=\"wp-image-2800\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/06\/13172732\/baby_foot.png\" alt=\"Blood from a newborn's foot is being placed on a card.\" width=\"350\" height=\"202\" \/><\/p>\n<p id=\"caption-attachment-2800\" class=\"wp-caption-text\">Figure 3. Taking a newborn blood sample for PKU testing. By Staff Sgt Eric T. Sheler, U.S. Air Force (Phenylketonuria testing) Public Domain<\/p>\n<\/div>\n<p>Even when influenced by the environment, phenotypes have a normal range of expression. For instance, human height varies based on nutrition and genetics, but not many people are shorter than 4\u00bd feet or taller than 7 feet. The range of phenotypic possibilities is called the <em>norm of reaction<\/em>. Hydrangeas, for example, may be blue, pink, or purple, but they are never naturally orange. Hydrangeas are blue in acidic soil with available aluminum, and they are pink in alkaline soil without available aluminum.<\/p>\n<p>You may have heard about PKU, a pleiotropic disorder caused by defects in a single gene coding for an enzyme that converts the amino acid phenylalanine to tyrosine. Newborns are tested for this defect very early in life (Figure 3), so that if the results are positive, they can be given a diet limiting phenylalanine ingestion. That way, the toxic buildup is prevented and the children can develop normally. PKU is an example in which environmental factors can modify gene expression.<\/p>\n<div class=\"textbox exercises\">\n<h3>Practice Question<\/h3>\n<p>Two identical twins (female) live in different parts of the country. One is very committed to a\u00a0healthy lifestyle: not smoking, exercising regularly, eating a diet rich in fresh produce, and avoiding red\u00a0meats and processed foods. The other is not as careful: she smokes, is overweight, and often eats fast\u00a0and processed foods. They are aware that several women in their family have had breast cancer, and\u00a0decide to consult a doctor about their odds of developing the disease. Which of the following statements\u00a0by the doctor sounds most correct?<\/p>\n<ol>\n<li>As identical twins, you are genetically the same, so your chances of developing breast cancer are identical.<\/li>\n<li>The twin with the healthy lifestyle should not be terribly concerned, while the one with the unhealthy lifestyle is at a higher risk.<\/li>\n<li>Breast cancer has a genetic component, and the twins have identical genes, so they have the same genetic risk. However, environmental factors such as smoking, obesity, and consumption of red meat have been shown to increase the risk of cancer. While both twins should monitor themselves closely, the twin who smokes and is overweight may want to consider a healthier lifestyle to decrease her risk of breast cancer.<\/li>\n<\/ol>\n<p><textarea aria-label=\"Your Answer\" rows=\"2\"><\/textarea><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q41921\">Show Answer<\/span><\/p>\n<div id=\"q41921\" class=\"hidden-answer\" style=\"display: none\">Option A is wrong; while\u00a0it has been shown that certain genes may predispose people to cancer, there are many\u00a0associations between environmental effects and cancer. Option B is also wrong; familial cancers have a genetic component which may or may not be balanced by a healthy lifestyle. Option C is the most correct answer; lifestyle choices are important, but genetic influences are to be taken seriously, especially if\u00a0there is a family pattern associated with them.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox learning-objectives\">\n<h3>In Summary: Effect of the Environment<\/h3>\n<p>While genes and genetic causes play a large role in health and phenotypes, the environment also plays an important role. Understanding this can enable the treatment of some disorders, such as the case with PKU in which limiting the intake of phenylalanine can prevent toxic build up of this amino acid. Often the norm of reaction is set by genetic factors but ultimately determined by environmental exposures.<\/p>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Check Your Understanding<\/h3>\n<p>Traits with ________ will often display a bell curve-shaped distribution when graphed.<\/p>\n<ul>\n<li>codominant inheritance<\/li>\n<li>continuous variation<\/li>\n<li>dominant-recessive inheritance<\/li>\n<\/ul>\n<details>\n<summary>Show Answer<\/summary>\n<p>continuous variation<\/p>\n<\/details>\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-2761\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Original<\/div><ul class=\"citation-list\"><li>Introduction to Genetics and the Environment. <strong>Authored by<\/strong>: Shelli Carter and Lumen Learning. <strong>Provided by<\/strong>: Lumen Learning. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em><\/li><\/ul><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>How do your genes and the environment interact?. <strong>Provided by<\/strong>: Genes in Life. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/www.genesinlife.org\/genes-your-health\/how-do-your-genes-and-environment-interact\">http:\/\/www.genesinlife.org\/genes-your-health\/how-do-your-genes-and-environment-interact<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em><\/li><li>Polygenic inheritance and environmental effects. <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\/polygenic-inheritance-and-environmental-effects\">https:\/\/www.khanacademy.org\/science\/biology\/classical-genetics\/variations-on-mendelian-genetics\/a\/polygenic-inheritance-and-environmental-effects<\/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><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><li>Application Spotlight: Effect of the Environment. <strong>Provided by<\/strong>: Open Learning Initiative. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/oli.cmu.edu\/jcourse\/workbook\/activity\/page?context=434a5f4180020ca600915a031e68a874\">https:\/\/oli.cmu.edu\/jcourse\/workbook\/activity\/page?context=434a5f4180020ca600915a031e68a874<\/a>. <strong>Project<\/strong>: Introduction to Biology (Open + Free). <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-2761-1\">Wood, A. R., Esko, T., Yang, J., Vedantam, S., Pers, T. H., Gustafsson, S., ... Frayling, T. M. (2014). Defining the role of common variation in the genomic and biological architecture of adult human height. <em>Nature Genetics<\/em>, <em>46<\/em>, 1173\u20131186. <a href=\"http:\/\/dx.doi.org\/10.1038\/ng.3097\" target=\"_blank\" rel=\"noopener\">http:\/\/dx.doi.org\/10.1038\/ng.3097<\/a>. <a href=\"#return-footnote-2761-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><li id=\"footnote-2761-2\">Lobo, I. (2008) <a href=\"#return-footnote-2761-2\" class=\"return-footnote\" aria-label=\"Return to footnote 2\">&crarr;<\/a><\/li><li id=\"footnote-2761-3\"><em>Ibid<\/em>. <a href=\"#return-footnote-2761-3\" class=\"return-footnote\" aria-label=\"Return to footnote 3\">&crarr;<\/a><\/li><li id=\"footnote-2761-4\">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-2761-4\" class=\"return-footnote\" aria-label=\"Return to footnote 4\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":7,"template":"","meta":{"_candela_citation":"[{\"type\":\"original\",\"description\":\"Introduction to Genetics and the Environment\",\"author\":\"Shelli Carter and Lumen Learning\",\"organization\":\"Lumen Learning\",\"url\":\"\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"\"},{\"type\":\"cc\",\"description\":\"How do your genes and the environment interact?\",\"author\":\"\",\"organization\":\"Genes in Life\",\"url\":\"http:\/\/www.genesinlife.org\/genes-your-health\/how-do-your-genes-and-environment-interact\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"\"},{\"type\":\"cc\",\"description\":\"Polygenic inheritance and environmental effects\",\"author\":\"\",\"organization\":\"Khan Academy\",\"url\":\"https:\/\/www.khanacademy.org\/science\/biology\/classical-genetics\/variations-on-mendelian-genetics\/a\/polygenic-inheritance-and-environmental-effects\",\"project\":\"\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"},{\"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\":\"\"},{\"type\":\"cc\",\"description\":\"Application Spotlight: Effect of the Environment\",\"author\":\"\",\"organization\":\"Open Learning Initiative\",\"url\":\"https:\/\/oli.cmu.edu\/jcourse\/workbook\/activity\/page?context=434a5f4180020ca600915a031e68a874\",\"project\":\"Introduction to Biology (Open + Free)\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2761","chapter","type-chapter","status-publish","hentry"],"part":3270,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/chapters\/2761","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":18,"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/chapters\/2761\/revisions"}],"predecessor-version":[{"id":6560,"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/chapters\/2761\/revisions\/6560"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/parts\/3270"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/chapters\/2761\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/wp\/v2\/media?parent=2761"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=2761"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/wp\/v2\/contributor?post=2761"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/wp-json\/wp\/v2\/license?post=2761"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}