Question

A normal woman, whose father was colour blind, is married to normal visioned man. Their sons would be

• A. 75% colour blind
• B. 50% colour blind
• C. 100% colour blind
• D. All normal

Answer 1

The correct option is B 50% colour blind

Colour blindness is X-linked recessive disorder. Father transmits his X chromosome to the daughters so the colour blind father will inherit his affected X chromosome to the daughter. Hence, the genotype of carrier female will be (X${}^c$X) and that of normal man will be (XY). The carrier female and normal man inherit the disease to 50% sons. Correct answer is option B.

Parent generation : "X${}^c$X" x "XY"

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