Question

which allele combination represents a male who has an x - linked recessive disorder?
$x^{r}y$
$x^{r}y$
$x^{r}x^{r}$
$x^{r}x^{r}$

Explanation:

• Males have one X and one Y chromosome.
• For an X - linked recessive disorder, if the allele on the X chromosome is recessive (\(x^{a}\)), since there is no second X chromosome to mask it (as in females \(x^{a}x^{a}\) for a recessive disorder), the male with \(x^{a}Y\) will express the disorder.
• \(x^{A}Y\) has a dominant allele on the X - chromosome, so the male will not have the recessive disorder.
• \(x^{a}x^{a}\) and \(x^{A}x^{a}\) are female genotypes (two X chromosomes).

Answer:

\(x^{a}Y\) (assuming \(x^{a}\) is the recessive allele for the X - linked disorder)