Of both normal parents, the chance of a male child becoming colour blind are

Options

A. no
B. possible only when all the four grand parents had normal vision
C. possible only when father's mother was colour blind
D. possible only when mother's father was colour blind

Answer

D

Explanation

Colour blindness is a X-linked recessive disease and the chance of a male child becoming colour blind of a normal parents is only when mother's father was colour blind.
This is criss-cross inheritance in which genes are transferred to a child from his material grandfather through his mother.