Hemophilia is an X‑linked recessive disorder represented by allele h (recessive) and H (normal). A carrier mother (XHXh) marries a normal‑vision male (XHY). What percentage of their sons will be affected and what percentage of their daughters will be carriers?
Answer
50% of the sons will be affected and 50% of the daughters will be carriers.
The correct answer is 50% of the sons will be affected and 50% of the daughters will be carriers. — Thus, 50% sons are normal and 50% are affected.
Step-by-step solution
- List the possible gametes from the mother: XH and Xh (each 50%).
- List the possible gametes from the father: X and Y (each 50%).
- Form a Punnett square combining these gametes.
- For daughters (receive X from father):
- - XH (mother) + X (father) → XHX (normal).
- - Xh (mother) + X (father) → XHXh (carrier).
- Thus, 50% daughters are normal and 50% are carriers.
- For sons (receive Y from father):
- - XH (mother) + Y → XHY (normal).
- - Xh (mother) + Y → XhY (affected).
- Thus, 50% sons are normal and 50% are affected.
Common mistake: Assuming the father contributes an X chromosome to sons, leading to a 25% calculation.
Concept tested: Sex‑linked inheritance
Published · How this solution was prepared and checked
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