If a woman is a carrier for the color-blind recessive allele and her husband is normal, what are their chances that a son will be color-blind?
A) None since the father is normal.
B) 50% since the mother is the only carrier.
C) 100% because the mother has the gene.
D) 25% because the mother is a hybrid.
E) None since he will also be just a carrier.

Question

Quizplus · Accepted Answer

Color blindness is an X-linked recessive trait. Since the mother is a carrier, she has one normal allele and one color-blind allele. The father, being normal, has only the normal allele on his X chromosome. Sons inherit their X chromosome from their mother and their Y chromosome from their father. Therefore, there is a 50% chance that a son will inherit the X chromosome carrying the color-blind allele from his mother, making him color-blind.

If a Woman Is a Carrier for the Color-Blind Recessive