Question

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

• A. $0.75$
• B. $1$
• C. $0$
• D. $0.5$

Answer 1

The correct option is C $0$

Colour-blind man ($X^c$Y) and normal woman (XX) can not have a colour-blind son as it is an X-linked recessive trait and is inherited by criss-cross inheritance. To have a colour-blind son, the mother should be a carrier ($X^c$X) or affected ($X^c{X}^c$) so as to pass the affected X chromosome to son.

Therefore, the correct answer is option C.