Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?
A) XnXn and XnY
B) XnXn and XNY
C) XNXN and XnY
D) XNXN and XNY
E) XNXn and XNY

Question

Quizplus · Accepted Answer

Since red-green color blindness is a sex-linked recessive trait, and the son is color-blind, he must have received a recessive allele (Xn) from his mother and a Y chromosome from his father. The mother must be a carrier (XNXn) because she has normal color vision but carries the recessive allele. The father has normal color vision and does not carry the recessive allele, so his genotype is XNY.

Red-Green Color Blindness Is a Sex-Linked Recessive Trait in Humans