Mendelian inheritance · USMLE Step 1

A child inherits two different mutant alleles of the same gene, one from each parent, resulting in disease expression. What is this called?

  1. Codominant allele expression
  2. Genetic anticipation over generations
  3. Compound heterozygosity
  4. Incomplete penetrance of the allele
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Correct answer: Compound heterozygosity

Compound heterozygosity occurs when two different pathogenic alleles of the same gene cause disease. This is common in recessive disorders. It is distinct from homozygosity for a single mutation.

Difficulty: Medium Question 16 of 20

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