{"id":214065,"date":"2025-06-16T08:13:21","date_gmt":"2025-06-16T08:13:21","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=214065"},"modified":"2025-06-16T08:14:00","modified_gmt":"2025-06-16T08:14:00","slug":"this-pedigree-chart-represents-the-inheritance-of-colour-blindness-in-humans-knowing-that-colour-blindness-is-a-sex-linked-recessive-disorder-if-individuals-il-1-and-il-2-have-another-boy-what-is-th","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/16\/this-pedigree-chart-represents-the-inheritance-of-colour-blindness-in-humans-knowing-that-colour-blindness-is-a-sex-linked-recessive-disorder-if-individuals-il-1-and-il-2-have-another-boy-what-is-th\/","title":{"rendered":"This pedigree chart represents the inheritance of colour blindness in humans Knowing that colour blindness is a sex-linked recessive disorder; if individuals Il-1 and Il-2 have another boy, what is the probability he will be colour blind"},"content":{"rendered":"\n

This pedigree chart represents the inheritance of colour blindness in humans Knowing that colour blindness is a sex-linked recessive disorder; if individuals Il-1 and Il-2 have another boy, what is the probability he will be colour blind? Express your answer as percent_<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

Correct Answer: 25%<\/strong><\/h3>\n\n\n\n

Explanation:<\/h3>\n\n\n\n

Key information:<\/strong><\/p>\n\n\n\n

    \n
  • Colour blindness is a sex-linked recessive<\/strong> trait, located on the X chromosome<\/strong>.<\/li>\n\n\n\n
  • Males<\/strong> (XY) express the trait if they inherit one affected X<\/strong> (they don\u2019t have a second X to compensate).<\/li>\n\n\n\n
  • Females<\/strong> (XX) must inherit two affected X chromosomes<\/strong> to express the trait but can be carriers<\/strong> if they have one affected X.<\/li>\n<\/ul>\n\n\n\n
    \n\n\n\n

    Step-by-step analysis:<\/h3>\n\n\n\n
      \n
    1. Individual II-1<\/strong> is a male<\/strong> (square) and not shaded<\/strong> \u2192 not colour blind<\/strong>, so his genotype is XY<\/strong> (normal X).<\/li>\n\n\n\n
    2. Individual II-2<\/strong> is a female<\/strong> (circle), not shaded<\/strong>, but she has a colour blind son<\/strong> (III-2), meaning she must be a carrier<\/strong> (X\u1d3aX\u1d9c).\n
        \n
      • Why? Because her son III-2 is colour blind (X\u1d9cY), and he must have inherited the X\u1d9c from his mother, as males inherit their Y from their father.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
      • Genotypes:<\/strong>\n
          \n
        • Father (II-1): X\u1d3aY (normal male)<\/li>\n\n\n\n
        • Mother (II-2): X\u1d3aX\u1d9c (carrier female)<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n
          \n\n\n\n

          Punnett square for a son<\/strong>:<\/h3>\n\n\n\n
          <\/th>X\u1d3a (Father)<\/th>Y (Father)<\/th><\/tr><\/thead>
          X\u1d3a (Mother)<\/td>X\u1d3aX\u1d3a<\/td>X\u1d3aY (normal son)<\/td><\/tr>
          X\u1d9c (Mother)<\/td>X\u1d3aX\u1d9c (carrier daughter)<\/td>X\u1d9cY (colour blind son<\/strong>)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

          So, for a son<\/strong>:<\/p>\n\n\n\n

            \n
          • 50% chance of inheriting X\u1d3a \u2192 X\u1d3aY \u2192 normal<\/li>\n\n\n\n
          • 50% chance of inheriting X\u1d9c \u2192 X\u1d9cY \u2192 colour blind<\/li>\n<\/ul>\n\n\n\n

            But the question asks if they have another boy<\/strong>, so we only consider male offspring<\/strong>:<\/p>\n\n\n\n

              \n
            • Among boys: 1 out of 2 will be colour blind = 50%<\/strong><\/li>\n<\/ul>\n\n\n\n

              However, the probability of the baby being a boy<\/strong> is 50%. So:<\/p>\n\n\n\n

              \n

              Final probability = 50% (chance of being male) \u00d7 50% (chance of being colour blind if male)
              = 25%<\/strong><\/p>\n<\/blockquote>\n\n\n\n

              \n\n\n\n

              Answer: 25%<\/strong> \u2705<\/h3>\n","protected":false},"excerpt":{"rendered":"

              This pedigree chart represents the inheritance of colour blindness in humans Knowing that colour blindness is a sex-linked recessive disorder; if individuals Il-1 and Il-2 have another boy, what is the probability he will be colour blind? Express your answer as percent_ The Correct Answer and Explanation is: Correct Answer: 25% Explanation: Key information: Step-by-step […]<\/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-214065","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/214065","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=214065"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/214065\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=214065"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=214065"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=214065"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}