Question

Colour blindness is a X linked recessive disorder in which the eye fails to distinguish between red and green colours. If a colour blind woman with genotype ($X^C{X}^C$) marries a normal visioned man (XY). Which among the following possibilities are true for their male children?

• A. All will be colour blind
• B. 75% possibility of being colour blind
• C. 50% possibility of being colour blind
• D. All will be normal visioned

Answer 1

The correct option is A All will be colour blind

$\bullet$ Colour blindness gene is X-linked (present only on the X chromosome) disorder. Inorder to get affected, an individual should have gene responsible for the defect in all the X chromosomes of their cell.
$\bullet$ Males have only one X chomosome, hence, defect in their single X chromosome can cause colour bindness.
$\bullet$ On the other hand, females have 2 X chromosomes, as a result ony defect in both the sex chomosomes can cause colour blindness in them. If only one X chromosome is affected, the female will be a carrier.

• Genotype of colour blind woman: undefined
• Genotype of carrier woman: undefined
• Genotype of colour blind man: $X^{c}Y$
• Genotype of normal visioned man: XY

The cross will be as follows:From the above cross we can deduce that all the sons will be colour blind and daughters will be carriers.