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

Question

Quizplus · Accepted Answer

Since the woman's father is color blind, she must have one X chromosome with the recessive allele for color blindness. The woman is a carrier. The man, being color blind, has the X chromosome with the recessive allele. Sons inherit their X chromosome from their mother and Y chromosome from their father. Therefore, there's a 50% chance the son will inherit the X chromosome with the recessive allele from his mother, making him color blind.

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