A recessive allele on the X chromosome is responsible for red-green color blindness in humans.A woman with normal vision whose father is color blind marries a color-blind male.What is the probability that this couple's first son will be color blind?

Question

Quizplus · Accepted Answer

The woman is a carrier of the color blindness allele on her X chromosome, because she has a normal vision allele on her other X chromosome. The father passes his color blindness allele to all of his daughters, who are then carriers, because he only has one X chromosome to pass on (males are always color-blind if they inherit the allele from their mother). The probability of the couple's first son being color-blind is 1/2, because there is a 50% chance of the mother passing on the color blindness allele and a 50% chance of the father passing it on. The probability of the son being color-blind is not affected by the fact that the couple's first child is a son instead of a daughter.

A Recessive Allele on the X Chromosome Is Responsible for Red-Green