Question

In which of the following conditions can the female progeny be colour blind?

• A. Father colour blind, mother carrier
• B. Father colourblind, mother normal
• C. Both normal
• D. Father normal, mother carrier

Answer 1

Answer: (A)

Colour blindness is a recessive sex-linked defect in which human beings are unable to distinguish red and green colours. Gene complement of a colour blind woman is $X^c{X}^c$ that of color blind man is $X^{c}Y$ and carrier woman with normal vision is $X{X}^c.$ A marriage between colour blind $\mathrm{man}\left(X^{c}Y\right)$ and carrier woman $\left(X{X}^c\right)$, results in $25\%$ carrier girls $\left(X{X}^c\right),25\%$ colour blind girls, $25\%$ normal sons $(XY)$ and $25\%$ colour blind sons. Colour blindness like any other trait, shows crisscross inheritance.