Question

A colourblind man marries a normal lady whose father was colourblind. If they produce two sons and two daughters, how many of them would suffer?

• A. Both sons
• B. Both daughters
• C. One son and one daughter
• D. Both sons and both daughters

Answer 1

Answer: (C)

One son and one daughter

Colour blindness is a X-linked recessive disorder.

Father transmit its X chromosome to the daughters so the colourblind father will pass the affected X chromosome to the daughter. Hence, the genotype of carrier female will be (X${}^c$X) and that of colour blind man will be (X${}^c$Y).

The marriage between carrier female and colourblind man will result in the expression of the disease in 1 son and 1 daughter. Correct answer is option C.

Parent generation : "X${}^c$X" X "X${}^c$Y"

Gametes : X${}^c$X--> X${}^c$Y	X${}^c$	X
X${}^c$	X${}^c$X${}^c$ colour blind girl	X${}^c$X carrier girl
Y	X${}^c$Y colour blind boy	XY normal boy

So, the correct answer is 'One son and one daughter'