Question

A colourblind man marries a woman with normal sight who has no history of colourblindness in her family. What is the probability of their son being colourblind?

• A. 0.5
• B. 1
• C. Nil
• D. 0.25

Hint:

In X-linked recessive traits like colorblindness, a son inherits his X chromosome from his mother. If the mother is not a carrier, the son cannot inherit the trait.

Answer 1

The Correct Option is C

Colorblindness is an X-linked recessive trait. The man is colorblind (X$^c$ Y), and the woman has normal sight with no family history of colorblindness (X X), so she is not a carrier. Their son inherits the Y chromosome from the father and one X from the mother. Since the mother can only pass a normal X, the son will be X Y (normal), and the probability of him being colorblind is 0, or nil.