Biology - Principles of Inheritance and Variation Question with Solution | TestHub

Color blindness is an X-linked recessive trait.

Let $X^C$ be the normal allele and $X^c$ be the colorblind allele.

The girl has normal vision but her father was colorblind ($X^{c}Y$). She must have inherited the $X^c$ chromosome from her father, making her genotype $X^C{X}^c$ (carrier).

The man has normal vision, so his genotype is $X^{C}Y$. The fact that his father was colorblind does not affect his genotype, as he inherits the Y chromosome from his father.

When they marry ($X^C{X}^c\times X^{C}Y$), the sons inherit the Y chromosome from the father and one of the X chromosomes from the mother.

The mother produces two types of gametes containing X chromosomes: $X^C$ and $X^c$ in equal proportion.

Therefore, the sons will have genotypes $X^{C}Y$ (normal vision) and $X^{c}Y$ (colorblind) in a $1:1$ ratio.

Thus, $50\%$ of the sons will be colorblind.

Answer: $50\%$ colourblind