Red-green colour-blindness in humans is a recessive X-linked trait. A man and a woman with normal vision have a colour-blind son. What is the probability that their next child will also be a colour-blind son?
A) 0
B) 1/4
C) 1/2
D) 3/4
E) 3/8

Question

Quizplus · Accepted Answer

Given that red-green color blindness is a recessive X-linked trait, and the parents have normal vision but have a color-blind son, it means the mother is a carrier (X^NX^c) and the father is normal (X^NY). For their next child to be a color-blind son, the child must inherit the X^c from the mother and the Y from the father. The probability of inheriting X^c from the mother is 1/2, and the probability of being a son (inheriting Y from the father) is also 1/2. Multiplying these probabilities gives 1/2 * 1/2 = 1/4.

Red-Green Colour-Blindness in Humans Is a Recessive X-Linked Trait