Color blindness is an X-linked recessive trait. A color-blind male and a female with normal vision, whose father was color-blind, have a child. What is the probability that their first-born child will be a color-blind male?

Core Concept

The mother is a carrier (X^C X^c) because her father was color-blind (X^c Y). The father is color-blind (X^c Y). The probability of having a male child is 1/2. For a male child to be color-blind, he must inherit the X^c chromosome from his carrier mother, which has a probability of 1/2. Multiplying these independent probabilities (1/2 × 1/2) yields a 25% chance.