Question

When a colour blind female offspring is born?

• A. Father is colour blind but mother is carrier
• B. Father is colour blind but mother is normal
• C. Father and mother both are normal
• D. Father is normal but mother is carrier.

Answer 1

The correct option is A Father is colour blind but mother is carrier

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${}^b$Y). Females with two copies of the affected gene show the disorder (X${}^b$X${}^b$). So, the female offspring to be colour blind, she should have both affected chromosomes. For this, father must be colour blind (X${}^b$Y) and mother could be carrier (X${}^b$X${}^B$) or colour blind (X${}^b$X${}^b$).

Parent generation : X${}^b$X${}^B$ x X${}^b$Y
c

Gametes : X${}^b$X${}^B$ ----> X${}^b$ X${}^B$ X${}^b$Y ----> X${}^b$ Y

Thus, the correct answer is option A.