Question

What is the inheritance of colour blindness of both parents having a normal vision but mother having a recessive gene for colour blindness?

• A. Son - 50% ; Daughter - nil
• B. Son - 100% ; Daughter - nil
• C. Son - nil ; Daughter - 100%
• D. Son - nil ; Daughter - nil

Answer 1

The correct option is A Son - 50% ; Daughter - nil

Colour blindness is a X-linked recessive disorder. One copy of the affected gene in males in each cell is sufficient to cause the disorder (X${}^c$Y). Females with two copies of the affected gene show the disorder (X${}^c$X${}^c$).

Females heterozygous (X${}^c$X) for this trait be normal but serve as a carrier of the disease.

According to the question, the female is carrier for colour blindness (X${}^c$X) and father is normal (XY). The carrier mother for colour blindness will inherit the disease to 50% sons (X${}^c$Y) while the 100% daughter will have normal vision. Correct answer is option A.