Pedigree analysis · USMLE Step 1

When analyzing a pedigree, why do geneticists often assume “complete penetrance” and “rare allele frequency” for a Mendelian trait?

  1. To simplify inference of the mode of inheritance
  2. Because all real traits are always fully penetrant and rare
  3. To allow analysis without knowing any actual genotypes
  4. Because environmental factors never influence gene expression
Show answer and explanation

Correct answer: To simplify inference of the mode of inheritance

Assuming complete penetrance and a rare allele simplifies pedigree analysis by removing confounders such as variable expression, incomplete penetrance, and common carriers. It is a simplifying assumption, not a claim about all real traits.

Difficulty: Medium Question 15 of 19

Practice all 19 Pedigree analysis questions

Keep practicing

More Pedigree analysis questions