In sex-linked inheritance, what is the genotype of females who are carriers for an X-linked recessive trait?

• A. X^a X^a
• B. X^A X^A
• C. X^A X^a
• D. X^A Y

Answer: (C)

Verified step by step guidance

1. Understand that sex-linked inheritance refers to genes located on the sex chromosomes, X and Y. In humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).
2. Recognize that an X-linked recessive trait means the trait is carried on the X chromosome and is recessive, meaning two copies of the recessive allele are needed for the trait to be expressed.
3. Identify that a female carrier for an X-linked recessive trait has one dominant allele and one recessive allele on her X chromosomes. This means she carries the trait but does not express it.
4. The genotype of a female carrier for an X-linked recessive trait is represented as \(X^A X^a\), where \(X^A\) is the dominant allele and \(X^a\) is the recessive allele.
5. Compare the given options: \(X^a X^a\) would express the trait, \(X^A X^A\) would not carry the trait, and \(X^A Y\) is a male genotype. Therefore, \(X^A X^a\) is the correct genotype for a female carrier.