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

Question

Quizplus · Accepted Answer

Color blindness is an X-linked recessive trait. Since the mother is a carrier (XcX), she has one normal allele (X) and one color-blind allele (c). The father, with normal vision, has only the normal allele (XY). A son inherits the Y chromosome from his father and one of the X chromosomes from his mother. If he inherits the X chromosome carrying the color-blind allele (c) from his mother, he will be color-blind. This gives a 50% chance, as the son could inherit either the mother's normal X or her color-blind X.

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