Question

which allele combination represents a male who has an x - linked recessive disorder?
○ $x^ry$
○ $x^ry$
○ $x^rx^r$
○ $x^rx^r$

Explanation:

1. Recall X - linked recessive inheritance in males: Males have sex chromosomes \(XY\). For an X - linked recessive disorder, the male needs the recessive allele (\(r\)) on his X chromosome (since he has only one X).
2. Analyze each option:

• Option \(X^{r}Y\): The X chromosome has the recessive allele (\(r\)) and the Y chromosome. Since males have \(XY\) and the recessive allele is on X, this male will express the X - linked recessive disorder.
• Option \(X^{R}Y\): The X chromosome has the dominant allele (\(R\)), so the male will not have the recessive disorder.
• Option \(X^{r}X^{r}\): This is the genotype of a female (two X chromosomes), not a male.
• Option \(X^{R}X^{r}\): This is also the genotype of a female (two X chromosomes), and she is a carrier (since she has one dominant and one recessive allele for an X - linked trait).

Answer:

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