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Analysis of X-Linked Dominant and Recessive Traits A young boy is color-blind. His one brother and five sisters are not. The boy has three maternal uncles and four maternal aunts. None of his uncles’ children or grandchildren is color-blind. One of the maternal aunts married a color-blind man, and half of her children, both male and female, are color-blind. The other aunts married men who have normal color vision. All their daughters have normal vision, but half of their sons are color-blind. a. Which of the boy’s four grandparents transmitted the gene for color blindness? b. Are any of the boy’s aunts or uncles color-blind? c. Is either of the boy’s parents color-blind?

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Human Heredity: Principles and Iss...

11th Edition
Michael Cummings
Publisher: Cengage Learning
ISBN: 9781305251052

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Section
BuyFindarrow_forward

Human Heredity: Principles and Iss...

11th Edition
Michael Cummings
Publisher: Cengage Learning
ISBN: 9781305251052
Chapter 4, Problem 17QP
Textbook Problem
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Analysis of X-Linked Dominant and Recessive Traits

A young boy is color-blind. His one brother and five sisters are not. The boy has three maternal uncles and four maternal aunts. None of his uncles’ children or grandchildren is color-blind. One of the maternal aunts married a color-blind man, and half of her children, both male and female, are color-blind. The other aunts married men who have normal color vision. All their daughters have normal vision, but half of their sons are color-blind.

  1. a. Which of the boy’s four grandparents transmitted the gene for color blindness?
  2. b. Are any of the boy’s aunts or uncles color-blind?
  3. c. Is either of the boy’s parents color-blind?

a.

Summary Introduction

To determine: The grandparents who transmitted the gene for color-blindness to the boy.

Introduction: The color-blind boy has three maternal uncles and four maternal aunts. The children and grandchildren of the boy’s uncle do not have color blindness. Only one of the boy’s maternal aunts married to a color-blind man and half of her children (including male and female) were color-blind. Other aunts married to men with normal vision and they have a normal daughter, but color-blind sons.

Explanation of Solution

Color-blindness is an X-linked recessive trait. It is commonly found in males. This is because the mother transmits X-chromosome to the son. If the mother carries the mutant chromosome, there is a 50% chance of having an affected son. However, if the father is normal and the mother carries one mutant allele, then daughters would be unaffected, but a carrier of the trait.

The boy is color-blind as per the data are given in the question. The genotype of the boy should be XcY. The father has transmitted Y allele to the boy. So, the trait for color blindness is not inherited from paternal grandparents...

b.

Summary Introduction

To determine: Whether the aunts and uncles of the boy are color-blind.

Introduction: The color-blind boy has three maternal uncles and four maternal aunts. The children and grandchildren of the boy’s uncle do not have color blindness. Only one of the boy’s maternal aunts married to a color-blind man and half of her children (including male and female) were color-blind. Other aunts married to men with normal vision and they have a normal daughter, but color-blind sons.

c.

Summary Introduction

To determine:  The parents of the boy are color-blind or not.

Introduction: The color-blind boy has three maternal uncles and four maternal aunts. The children and grandchildren of the boy’s uncle do not have color blindness. Only one of the boy’s maternal aunts married to a color-blind man and half of her children (including male and female) were color-blind. Other aunts married to men with normal vision and they have a normal daughter, but color-blind sons.

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