Question

which allele combination represents a male who has an x - linked recessive disorder? \\(\bigcirc\\) \\(x^ry\\) \\(\bigcirc\\) \\(x^ry\\) \\(\bigcirc\\) \\(x^rx^r\\) \\(\bigcirc\\) \\(x^rx^r\\)

Explanation:

• Males have the sex - chromosome combination \(XY\).
• For an X - linked recessive disorder, the allele on the \(X\) chromosome must be recessive. Let the recessive allele be \(X^{r}\) and the dominant allele be \(X^{R}\).
• In option \(X^{r}Y\), the male has a recessive allele on the \(X\) chromosome. Since males have only one \(X\) chromosome, if that \(X\) has the recessive allele for an X - linked recessive disorder, they will express the disorder.
• Option \(X^{R}Y\) has a dominant allele on the \(X\) chromosome, so the male will not have the X - linked recessive disorder.
• Options \(X^{r}X^{r}\) and \(X^{R}X^{r}\) are for females (because of the two \(X\) chromosomes).

Answer:

A. \(X^{r}Y\)