Mendelian inheritance · USMLE Step 1

A mother with an X-linked dominant disorder has a child with an unaffected partner. What proportion of daughters will be affected?

  1. 0%
  2. 25%
  3. 50%
  4. 100%
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Correct answer: 50%

A heterozygous affected mother passes the dominant allele to 50% of daughters. Both sons and daughters have a 50% chance of inheriting the mutation. The unaffected parent contributes a normal allele.

Difficulty: Medium Question 19 of 20

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