A man expresses a certain X-linked recessive genetic disorder. Which of the following must be...
BIOLOGY
SAT 2021
A man expresses a certain X-linked recessive genetic disorder. Which of the following must be true? I. His father passed on the allele for the disorder II. His mother passed on the allele for the disorder III. His mother expresses the disorder
- A. None of these
- B. I only
- C. II and III only
- D. II only
Correct Answer: B. I only
Explanation
As the disorder is X-linked and the subject is male, he only received an X-chromosome from his mother. Therefore, the allele for the disorder must have been inherited from his mother. However, this does not mean that the mother expressed the disorder herself, as she could have the dominant allele in addition to one recessive allele.
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