Mendelian inheritance · USMLE Step 1

A woman who is a carrier for an X-linked recessive disease has a child with a healthy male partner. What is the chance that she will have an affected son?

  1. 25%
  2. 50%
  3. 75%
  4. 100%
Show answer and explanation

Correct answer: 50%

A carrier mother has a 50% chance of passing the mutant X allele. Sons who inherit the allele will be affected because they have only one X chromosome.

Difficulty: Medium Question 3 of 20

Practice all 20 Mendelian inheritance questions

Keep practicing

More Mendelian inheritance questions