Principle of Inheritance and VariationEasyBloom L3
Question
A woman with normal vision, but whose father was colour blind, marries a colour-blind man. Suppose that the fourth child of this couple was a boy. This boy
Options
A.may be colour blind or may be of normal vision
B.must be colour blind
C.must have normal colour vision
D.will be partially colour blind since he is heterozygous for the colour blind mutant allele
Solution
Sol.(a) [Key Concept: X-linked Colour Blindness — Carrier Mother] The woman's father was colour blind (Xc Y), so she inherited Xc from father → she is a carrier (XC Xc). She marries a colour-blind man (Xc Y). Cross: XC Xc × Xc Y → sons: XC Y (normal vision) or Xc Y (colour blind) in 1:1. So any son of this couple has a 50% chance of being colour blind and 50% chance of normal vision. The fourth child being a boy still has 50:50 chance — (a) is correct.
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