Penetrance

Probability that an allele responsible for a trait actually expresses it.

📖 Full definition

Not every carrier of an allele develops the associated trait. Penetrance is the fraction of carriers who express it. 100% penetrance means every carrier shows the trait; below that, penetrance is incomplete (the case for many genetic conditions).

💡 Concrete example

The BRCA1 gene, linked to breast cancer, has ~70% penetrance: 70% of female carriers will develop cancer by age 80.

🔗 See also

Expressivity →
Dominant gene →
Allele →

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