Question

A colour blind son is born to normal parents. Is shows that.

• A. The father was heterozygous for colour blindness
• B. The mother was genotypically homozygous
• C. The mother was heterozygous for colour blindness
• D. Both parents carried a recessive gene for the disorder

Answer 1

Answer: (C)

The mother was heterozygous for colour blindness

Colour blindness is a sex-linked disorder whose gene is located on the X chromosome. So, it is carried by the normal females not expressing the disease. If a colour blind child is born to a normal couple, then mother would be the carrier and the child would be male.

The above picture shows the inheritance of colour blindness.

So, the correct answer is 'The mother was heterozygous for colour blindness'.