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

'X'- linked traits in male are inherited to his daughters, but not his sons. The daughters of color-blind man receive one 'X' chromosome from father and the another from mother. The sons receive 'X' chromosome from mother and 'Y' chromosome from father. The sons of color-blind man and homozygous normal vision woman get normal vision.