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

The correct option is A

her father and maternal grandfather are colour blind.

The correct option is A.

Explanation of correct option:

1. Colour blindness is a type of disorder in which the person faces trouble in seeing or identifying specific colors like red, blue, and green.
2. They also have difficulties identifying the differences between color shades.
3. Colour blindness is caused by genes located on the X chromosome.
4. It is a recessive disorder since it occurs when an individual has defects in all the X chromosomes of the cell.
5. Females inherit one X chromosome from each parent; hence they can be either homozygous or heterozygous.
6. A color-blind girl is born only when her father is color blind, and her mother is a carrier.
7. If the maternal grandfather is color blind, the mother will be a carrier.

Final answer: A color blind girl is rare because she will be born only when her father and maternal grandfather are color blind.