Question

which allele combination represents a female who is heterozygous for a sex - linked trait?
○ ( x ^ { r } y )
○ ( x ^ { r } y )
○ ( x ^ { r } x ^ { r } )
○ ( x ^ { r } x ^ { r } )

Explanation:

• Females have two X chromosomes (\(X^{R}X^{r}\), \(X^{R}X^{R}\), etc.), while males have one X and one Y chromosome (\(X^{R}Y\), \(X^{r}Y\)).
• Heterozygous means having two different alleles. So for a sex - linked trait in females, it should be \(X^{R}X^{r}\) (one dominant \(R\) allele and one recessive \(r\) allele on the X chromosomes). \(X^{R}X^{R}\) is homozygous dominant, \(X^{R}Y\) and \(X^{r}Y\) are male genotypes.

Answer:

\(X^{R}X^{r}\) (the third option)