Pedigree analysis · USMLE Step 1

Which assumption is typically made when performing classic pedigree analysis under Mendelian inheritance models?

The disease allele is at high frequency in the population
Incomplete penetrance is assumed to be present in every case
The trait is rare, so those marrying in seldom carry the allele
Many different genes each contribute equally to the phenotype

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Correct answer: The trait is rare, so those marrying in seldom carry the allele

Classic Mendelian pedigree analysis assumes the trait is rare, so unrelated individuals who marry into the family are unlikely to carry the mutant allele. This simplifies inferring the mode of inheritance.

Difficulty: Medium Question 6 of 19

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