Q. A woman with normal vision, but whose father was colour blind, marries a colourblind man. Suppose that the fourth child of this couple was a boy. This boy :
A) must have normal colour vision
B) will be partially colourblind since he is heterozygous for the colourblind mutant allele
C) must be colourblind
D) may be colourblind or may be of normal vision
Explanation
[Solution from source] The woman got her colour-blind father's X, so she is a carrier (XᶜX). A son always gets his X from his mother, so each son has a 50% chance of colour blindness, whatever the birth order. Males carry only one X, so a son cannot be heterozygous. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.