A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind has children with a color-blind male. What is the probability that this couple's first son will be color blind?
A) 1/4
B) 1/2
C) 2/3
D) 3/4

Question

Quizplus · Accepted Answer

Since the woman has a color-blind father, she must carry one allele for color blindness (Xc) because the trait is X-linked and her father would have passed his only X chromosome to her. The woman's genotype is XcX. The color-blind male has the genotype XcY. When they have a son, the son gets a Y chromosome from his father and either an X or Xc chromosome from his mother. There's a 50% chance he will inherit the Xc from his mother, leading to color blindness.

A Recessive Allele on the X Chromosome Is Responsible for Red-Green