A recessive allele on the X chromosome causes color deficiency. A noncolor-deficient woman (whose father is color deficient) marries a color-deficient man. If they have a son, what is the chance that he will be color deficient?
A) 75%
B) 100%
C) 25%
D) 50%
E) 0%

Question

Quizplus · Accepted Answer

The son inherits his X chromosome from his mother and his Y chromosome from his father. Since the mother is not color deficient but her father is, she must be a carrier of the recessive allele (X^CX^c). The father, being color deficient, has the genotype X^cY. Therefore, the son can either inherit the X^C (normal vision) or X^c (color deficient) allele from his mother. This results in a 50% chance of being color deficient.

A Recessive Allele on the X Chromosome Causes Color Deficiency