To determine which allele combination represents a female who is heterozygous for a sex-linked trait, let’s first break down the concepts involved.
### Key Concepts
1. Sex Chromosomes and Gender:
- Females have two X chromosomes (XX).
- Males have one X and one Y chromosome (XY).
2. Heterozygosity:
- Heterozygous means having two different alleles for a particular gene.
- In the context of sex-linked traits (those found on the X chromosome), this would mean one allele on each of the two X chromosomes in females.
### Options Analysis
1. Option 1: [tex]\(X^R Y\)[/tex]
- This combination has one X chromosome and one Y chromosome.
- It represents a male genotype, not a female.
2. Option 2: [tex]\(X^{\prime} Y\)[/tex]
- This combination also has one X chromosome and one Y chromosome.
- It represents a male genotype, not a female.
3. Option 3: [tex]\(X^R X^r\)[/tex]
- This combination has two X chromosomes.
- It contains two different alleles ([tex]\(X^R\)[/tex] and [tex]\(X^r\)[/tex]), making it heterozygous.
- This fits the criteria for a female who is heterozygous for a sex-linked trait.
4. Option 4: [tex]\(X^R X^R\)[/tex]
- This combination has two X chromosomes.
- It contains two identical alleles ([tex]\(X^R\)[/tex] and [tex]\(X^R\)[/tex]), making it homozygous.
- This does not fit the criteria for being heterozygous.
### Conclusion
Based on the analysis, the allele combination that represents a female who is heterozygous for a sex-linked trait is [tex]\(X^R X^r\)[/tex].
Thus, the correct answer is:
[tex]\[ X^R X^r \][/tex]
