A color-blind man and a woman with normal vision whose father was color blind have a son. Color blindness, in this case, is caused by an X-linked recessive gene. If only the male offspring are considered, the probability that their son is color-blind is ____.
A)25 percent
B)50 percent
C)75 percent
D)100 percent
E)0 percent

Question

Quizplus · Accepted Answer

Since color blindness is caused by an X-linked recessive gene, the son must inherit the gene from his mother (who is a carrier) and the affected grandfather (who has the gene). Therefore, the probability of the son being color-blind is equal to the probability of inheriting the gene from the mother, which is 50 percent since she is a carrier.

A Color-Blind Man and a Woman with Normal Vision Whose