Question

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

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 the X - chromosome and Y - chromosome).

Step2: Determine Gametes

• The mother (\(X^{B}X^{B}\)) can only produce gametes with the \(X^{B}\) allele.
• The father (\(X^{b}Y\)) can produce two types of gametes: \(X^{b}\) and \(Y\).

Step3: Analyze Male Offspring Genotypes

When considering male offspring, they inherit the Y - chromosome from the father and an X - chromosome from the mother. Since the mother only gives \(X^{B}\) and the father gives Y for male offspring, the genotype of male children will be \(X^{B}Y\).

Step4: Determine Color - Blindness in Males

Color - blindness (for X - linked recessive traits like color - blindness) in males occurs when they have the recessive allele (\(X^{b}\)) on their X - chromosome. Since male children have \(X^{B}Y\) (dominant allele for normal vision on the X - chromosome), none of the male children will be color - blind. So the proportion of male children that are color - blind is \(0\%\).

Answer:

B. 0%