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 (XX), males have XY.
• Heterozygous means having two different alleles.
• \( X^R X^r \) has two different alleles (\( R \) and \( r \)) on the X chromosomes, fitting a heterozygous female for a sex - linked trait. \( X^R Y \) and \( X^r Y \) are male genotypes. \( X^R X^R \) is homozygous female.

Answer:

\( \boldsymbol{X^R X^r} \) (the option with \( X^R X^r \))