Question

A normal woman whose father was colourblind marries a normal man. Her sons would be

• A. 75% colourblind
• B. 50% colour blind
• C. All normal
• D. All colour blind.

Answer 1

The correct option is B 50% colour blind

Colour blindness is a X-linked recessive disorder. If the father of a normal women is colour blind then she will be a carrier of the disease, since she will receive one X chromosome from both her parents and the X chromosome from the father will be diseased. If she now marries a normal man then there will be 50% chances of her sons being colourblind. Since the son will receive the X chromosome from the mother and the Y chromosome from the father and one of the X chromosomes in the mother is normal and the other diseased. If the child receives the normal X chromosome (50% chances) then he will not have the disease and if he receives the diseased chromosome (50%) then he will have the disease. So, the correct option is '50% colour blind'.