Rakesh's parents have normal colour vision. But his maternal grandfather is colour -blind. What is the possibility of Rakesh and his siblings becoming colour-blind?

Explanation

1. Data given: Rakesh's maternal grandfather is colour-blind, therefore he is `x^(c)Y`. His daughter would be carrier for colour-blindness. Therefore, Rakesh's mother will be `X^(c)C`.
2. Rakesh's father is normal, therefore his genotype will be XY. Upon crossing a carrier woman with normal man we obtain following result: `X^(c)X` with `XY=X^(c)Y,X^(c)X,XX,XY`
3. Since colour-blindness shows criss-cross inheritance, Rakesh and his brothers stand a 50% possibility of being colour-blind, while his sisters also have 50% possibility of becoming carriers of the disorder.