Question

A colour-blind girl is rare because she will be born only when:

• A. Her mother and maternal grandfather were colour blind.
• B. Her father and maternal grandfather were colour blind.
• C. Her mother is colour blind and father has normal vision.
• D. Parents have normal vision but grandparents were colour blind.

Answer 1

Answer: (B)

Colour blindness is a recessive sex-linked trait in which the eyes fails to distinguish red and green colours. The gene for normal vision is dominant. The genotype of the mother has to be either X^C X^C or X^CX and that of father X^CY so that the daughter becomes colour-blind.