{"id":220897,"date":"2025-05-29T03:35:08","date_gmt":"2025-05-29T03:35:08","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=220897"},"modified":"2025-05-29T03:35:10","modified_gmt":"2025-05-29T03:35:10","slug":"dihybrid-crosses-2","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/05\/29\/dihybrid-crosses-2\/","title":{"rendered":"Dihybrid Crosses"},"content":{"rendered":"\n<p>Dihybrid Crosses 1. In man, assume that spotted skin (S) is dominant over non-spotted skin (s) and that wooly hair (W) is dominant over non-wooly hair (w). Cross a marriage between a heterozygous spotted, non-wooly man with a heterozygous wooly-haired, non-spotted woman. Give genotypic and phenotypic ratios of offspring. 2. In horses, black is dependent upon a dominant gene, B, and chestnut upon its recessive allele, b. The trotting gait is due to a dominant gene, T, the pacing gait to its recessive allele, t. If a homozygous black pacer is mated to a homozygous chestnut trotter, what will be the appearance of the F1 generation? 3. In mice, the ability to run normally is a dominant trait. Mice with this trait are called running mice (R). The recessive trait causes mice to run in circles only. Mice with this trait are called waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over brown hair (b). For each of the following problems, determine the parent genotypes, determine possible gametes then construct a Punnet square to solve. a. Cross a heterozygous running, heterozygous black mouse with a homozygous running, homozygous black mouse. List all of the possible phenotypes from this cross. Pedigrees Shaded individuals have Huntington&#8217;s Disease 1. Write the generation on the pedigree numbers (roman numerals). 2. Which members of the family above are afflicted with Huntington&#8217;s Disease? 3. There are no carriers for Huntington&#8217;s Disease- you either have it or you don&#8217;t. With this in mind, is Huntington&#8217;s disease caused by a dominant or recessive trait?<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-1-color\">The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Dihybrid Crosses<\/strong><\/h2>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1. Spotted Skin and Wooly Hair in Humans<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Traits:<\/strong>\n<ul class=\"wp-block-list\">\n<li>Spotted skin (S) is <strong>dominant<\/strong> to non-spotted skin (s)<\/li>\n\n\n\n<li>Wooly hair (W) is <strong>dominant<\/strong> to non-wooly hair (w)<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Man\u2019s genotype<\/strong>: Heterozygous spotted, non-wooly \u2192 <strong>Ssww<\/strong><\/li>\n\n\n\n<li><strong>Woman\u2019s genotype<\/strong>: Heterozygous wooly-haired, non-spotted \u2192 <strong>ssWw<\/strong><\/li>\n\n\n\n<li><strong>Gametes from Man (Ssww)<\/strong>: Sw, sw<\/li>\n\n\n\n<li><strong>Gametes from Woman (ssWw)<\/strong>: sW, sw<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th><\/th><th>sW<\/th><th>sw<\/th><\/tr><\/thead><tbody><tr><td><strong>Sw<\/strong><\/td><td>SsWw<\/td><td>Ssww<\/td><\/tr><tr><td><strong>sw<\/strong><\/td><td>ssWw<\/td><td>ssww<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p><strong>Genotypic outcomes:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>SsWw: 1<\/li>\n\n\n\n<li>Ssww: 1<\/li>\n\n\n\n<li>ssWw: 1<\/li>\n\n\n\n<li>ssww: 1<\/li>\n<\/ul>\n\n\n\n<p><strong>Genotypic ratio:<\/strong> 1:1:1:1<\/p>\n\n\n\n<p><strong>Phenotypic outcomes:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>SsWw \u2192 <strong>Spotted, Wooly<\/strong><\/li>\n\n\n\n<li>Ssww \u2192 <strong>Spotted, Non-wooly<\/strong><\/li>\n\n\n\n<li>ssWw \u2192 <strong>Non-spotted, Wooly<\/strong><\/li>\n\n\n\n<li>ssww \u2192 <strong>Non-spotted, Non-wooly<\/strong><\/li>\n<\/ul>\n\n\n\n<p><strong>Phenotypic ratio:<\/strong> 1 Spotted Wooly : 1 Spotted Non-wooly : 1 Non-spotted Wooly : 1 Non-spotted Non-wooly<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2. Horses: Coat Color and Gait<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>B = Black<\/strong>, <strong>b = Chestnut<\/strong><\/li>\n\n\n\n<li><strong>T = Trotting<\/strong>, <strong>t = Pacing<\/strong><\/li>\n\n\n\n<li><strong>Parents:<\/strong>\n<ul class=\"wp-block-list\">\n<li>Homozygous black pacer \u2192 <strong>BBtt<\/strong><\/li>\n\n\n\n<li>Homozygous chestnut trotter \u2192 <strong>bbTT<\/strong><\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>F1 Genotype:<\/strong> All offspring = <strong>BbTt<\/strong><\/li>\n\n\n\n<li><strong>Phenotype:<\/strong>\n<ul class=\"wp-block-list\">\n<li>All offspring are <strong>Black<\/strong> (due to B) and <strong>Trotting<\/strong> (due to T)<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>F1 appearance: All Black Trotters<\/strong><\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3. Mice: Running &amp; Hair Color<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Running (R)<\/strong> is dominant over <strong>Waltzing (r)<\/strong><\/li>\n\n\n\n<li><strong>Black hair (B)<\/strong> is dominant over <strong>Brown hair (b)<\/strong><\/li>\n\n\n\n<li><strong>Cross:<\/strong>\n<ul class=\"wp-block-list\">\n<li>Heterozygous running, heterozygous black \u2192 <strong>RrBb<\/strong><\/li>\n\n\n\n<li>Homozygous running, homozygous black \u2192 <strong>RRBB<\/strong><\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Gametes:<\/strong>\n<ul class=\"wp-block-list\">\n<li>RrBb \u2192 RB, Rb, rB, rb<\/li>\n\n\n\n<li>RRBB \u2192 All RB<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Punnett Square:<\/strong><\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th><\/th><th>RB (from RRBB)<\/th><\/tr><\/thead><tbody><tr><td><strong>RB<\/strong><\/td><td>RRBB<\/td><\/tr><tr><td><strong>Rb<\/strong><\/td><td>RRBb<\/td><\/tr><tr><td><strong>rB<\/strong><\/td><td>RrBB<\/td><\/tr><tr><td><strong>rb<\/strong><\/td><td>RrBb<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p><strong>Genotypes:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>RRBB, RRBb, RrBB, RrBb<\/li>\n<\/ul>\n\n\n\n<p><strong>All phenotypes:<\/strong> <strong>Running, Black<\/strong><\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>All offspring will be Running with Black hair<\/strong><\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Pedigrees \u2013 Huntington\u2019s Disease<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1. Generations:<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use <strong>Roman numerals<\/strong> for each generation:\n<ul class=\"wp-block-list\">\n<li>Top row: <strong>I<\/strong><\/li>\n\n\n\n<li>Second row: <strong>II<\/strong><\/li>\n\n\n\n<li>Third row: <strong>III<\/strong>, and so on.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2. Afflicted Members:<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Shaded individuals<\/strong> are affected by Huntington\u2019s Disease.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3. Is Huntington&#8217;s Disease Dominant or Recessive?<\/strong><\/h3>\n\n\n\n<p><strong>Answer:<\/strong> <strong>Huntington\u2019s Disease is caused by a dominant trait.<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong> Explanation:<\/strong><\/h3>\n\n\n\n<p>Huntington\u2019s Disease is a neurodegenerative genetic disorder that is inherited in an <strong>autosomal dominant<\/strong> pattern. This means that a person only needs <strong>one copy of the mutant gene<\/strong> to develop the disease. In a pedigree, this pattern is often easily recognizable because the disease appears in <strong>every generation<\/strong> and affects both males and females equally.<\/p>\n\n\n\n<p>There are <strong>no carriers<\/strong> of Huntington\u2019s Disease. If someone carries the gene, they will eventually develop the condition, typically in middle adulthood. This is different from <strong>recessive disorders<\/strong>, where individuals can carry a defective gene without showing symptoms because they also possess one normal gene.<\/p>\n\n\n\n<p>In dominant inheritance, when an individual with Huntington\u2019s (Hh) has children with someone who does not have the gene (hh), there is a <strong>50% chance<\/strong> that each child will inherit the disease. If a person in the pedigree has Huntington\u2019s Disease and at least one of their parents also had it, this supports dominant inheritance.<\/p>\n\n\n\n<p>Recessive conditions, by contrast, often <strong>skip generations<\/strong>, and two unaffected parents can have an affected child if both are carriers. In Huntington\u2019s pedigrees, affected individuals <strong>do not skip generations<\/strong>, confirming its dominant nature.<\/p>\n\n\n\n<p>Furthermore, since Huntington\u2019s is linked to a mutation in the <strong>HTT gene on chromosome 4<\/strong>, which is autosomal, the trait is <strong>not sex-linked<\/strong>, again supporting autosomal dominant inheritance. Genetic testing and family history are the main tools for diagnosis and confirmation.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/05\/learnexams-banner7-78.jpeg\" alt=\"\" class=\"wp-image-220898\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Dihybrid Crosses 1. In man, assume that spotted skin (S) is dominant over non-spotted skin (s) and that wooly hair (W) is dominant over non-wooly hair (w). Cross a marriage between a heterozygous spotted, non-wooly man with a heterozygous wooly-haired, non-spotted woman. Give genotypic and phenotypic ratios of offspring. 2. In horses, black is dependent [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-220897","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/220897","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=220897"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/220897\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=220897"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=220897"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=220897"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}