Question

A colour blind man marries a daughter of colour blind father, then in the offsprings

• A. All sons are colour blind
• B. All daughters are colour blind
• C. Half sons are colour blind
• D. No daughter is colour blind

Answer 1

The correct option is C Half sons are colour blind

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 colour blind man will be (X${}^c$Y). The carrier female and colour blind man will inherit the disease to 50% sons and 50% daughters. 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