Red-green color blindness is an X-linked recessive trait in humans. Two people with normal color vision have a son with colorblindness. Given this information, the genotypes of the parents are ________.
A) XnXn and XnY
B) XNXN and XnY
C) XNXN and XNY
D) XNXn and XNY

Question

Quizplus · Accepted Answer

Since red-green color blindness is an X-linked recessive trait, the son must have inherited his Y chromosome from his father and the X chromosome carrying the colorblindness allele (Xn) from his mother. For the son to express colorblindness, his mother must be a carrier of the trait (XNXn), and his father must have normal color vision (XNY), as men only have one X chromosome, which in this case does not carry the colorblindness allele.

Red-Green Color Blindness Is an X-Linked Recessive Trait in Humans