Question

look at this cross: $x^b x^b$ x $x^b y$ what proportion/percent of the male children are colorblind? 25% 100% 75% 0%

Explanation:

Step1: Analyze Parental Genotypes

The mother's genotype is $X^B X^B$ (homozygous dominant for normal vision), and the father's genotype is $X^b Y$ (hemizygous for color - blindness allele on X - chromosome and Y - chromosome).

Step2: Determine Gametes

• Mother ($X^B X^B$) can only produce gametes with $X^B$ (since both X - chromosomes have the $B$ allele).
• Father ($X^b Y$) can produce two types of gametes: $X^b$ (from the X - chromosome) and $Y$ (from the Y - chromosome).

Step3: Analyze Offspring Genotypes for Males

When we combine the gametes, for male offspring, they inherit the Y - chromosome from the father and an X - chromosome from the mother. Since the mother only gives $X^B$ chromosomes, the genotype of male offspring will be $X^B Y$.

Step4: Determine Proportion of Color - Blind Males

Color - blindness (in the context of X - linked inheritance) is associated with the $b$ allele. Since male offspring have the genotype $X^B Y$ (no $b$ allele), the proportion of male children that are color - blind is 0%.

Answer:

0% (corresponding to the option "0%")