If a colour-blind man marries a woman who is homozygous for normal colour vision, the probability of their son being colour-blind is

A colour-blind man (\( X^cY \)) and a homozygous normal vision woman (\( X^CX^C \)) produce daughters who are carriers (\( X^CX^c \)) and sons with normal vision (\( X^CY \)). Thus, probability of their son being colour-blind is 0.