Question

look at this cross: x^b x^b x x^b y
what proportion of the male children are colorblind?
100%
50%
75%
25%

Explanation:

Step1: Analyze X - linked inheritance

In X - linked inheritance, males inherit their X chromosome from their mother and Y from their father. The mother's genotype is $X^{B}X^{b}$ and the father's is $X^{B}Y$.

Step2: Determine male offspring genotypes

For male children, they get the Y chromosome from the father and an X chromosome from the mother. The mother can pass on $X^{B}$ or $X^{b}$. So the possible genotypes of male children are $X^{B}Y$ (normal) and $X^{b}Y$ (colorblind).

Step3: Calculate the proportion

There are 2 possible genotypes for male children, and 1 of them ($X^{b}Y$) is colorblind. So the proportion is $\frac{1}{2}$ or 50%.

Answer:

50% (corresponding to the option with 50%)