Question

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. 1
• B. \N
• C. 0.5
• D. 0.75

Answer 1

The correct option is B \N

Red-green colour blindness is a recessive sex-linked trait in which the eye fails to distinguish between red and green colour. The gene for colour blindness is present on the X chromosome.

(c = gene for colour blindness and C = gene for normal vision)

Females are colour blind when both the X chromosomes carry genes for colour blindness (XcXc). However, males are colourblind with just a single copy of the gene for colour blindness. (XcY).

Son receives X chromosome from the mother and Y chromosome from the father.

As per the scenario given in the question, mother is homozygous for normal colour vision and hence there is no chance that son can suffer from colour blindness.

Thus, if a colourblind man marries a woman who is homozygous for normal colour vision, the probability of their son being colourblind is zero.


Option B is the correct answer.