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Q.
In which of the following conditions can the female progeny be colour blind?
Principles of Inheritance and Variation
Solution:
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 $\operatorname{man}\left(X^{c} Y\right)$ and carrier woman $\left( XX ^{ c }\right)$, results in $25 \%$ carrier girls $\left( XX ^{ c }\right), 25 \%$ colour blind girls, $25 \%$ normal sons $( XY )$ and $25 \%$ colour blind sons. Colour blindness like any other trait, shows crisscross inheritance.