Question

A normal woman whose father was colour blind is married to a normal man. The sons would be

• A. 75% colourblind
• B. 50% colourblind
• C. All normal
• D. All colourblind

Answer 1

Answer: (B)

50% colourblind

Colour blindness is a X-linked recessive disorder. Father transmit its X chromosome to the daughters so the colour blind father will inherit its 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 will transmit 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 girl
Y	X${}^c$Y colour blind boy	XY normal boy