Correct Answer - A
If a colourblind man marries a woman who is homozygous for normal colour vision, the probaility of their son being colourblind is zero. Colour blindness is a recessive sex-linked trait in which the eye fails to distinguish between appears only when both sex chromosomes carry recessive gene `(X^(c) X^(c))`. However, in human males, the defect appears due to single recessive gene `(X^(c) Y)` because Y chromosome does not carry gene for colour vision. This disease shows criss-cross inheritance.
Thus, there is zero probability of son being colourblind. Hence, option (a) is correct.
