Question

A normal vision female whose father is colour-blind marries a normal vision male. What would be the probability of her sons and daughters to be color blind?

• A. 50% sons colour blind and all daughters with phenotypically normal vision
• B. 50% sons colour blind and 50% daughter normal
• C. 50% sons colour blind and 50% daughter colour blind
• D. All sons normal and 50% colour blind daughter

Answer 1

Answer: (A)

50% sons colour blind and all daughters with phenotypically normal vision

• Since the father of the woman is colour blind, the woman would be a carrier of the trait.

Mother Father

$X^c$ $X$ x $X$ $Y$

$X^c$ $X$

$X$ $X^c$ $X$ $X$ $X$

$Y$ $X^c$$Y$ $X$ $Y$

• If she marries a normal vision man, then by the method of punnet square, we can say that half of the boys will be colour blind, half boys will have normal vision and half of the girl will be carriers and another half would not have the colour-blind gene. However, all girls will be phenotypically normal.

So the correct answer is option A.