A recessive allele on the X chromosome causes color blindness. A noncolor-blind woman (whose father is color blind)marries a color-blind man. What is the chance that their son will be color blind?

Question

Quizplus · Accepted Answer

Since the noncolor-blind woman's father is color-blind, she must be a carrier of the recessive allele. The color-blind man has the recessive allele on his X chromosome. Therefore, the possible genotypes of the parents are X^B X^b (woman) and X^b Y (man). The Punnett square for this cross is:

| X^B | X^b
---|---|---
X^b | X^B X^b | X^b X^b
Y | X^b Y | X^b Y

Thus, there is a 50% chance that their son will inherit the recessive allele and be color-blind.

A Recessive Allele on the X Chromosome Causes Color Blindness