WANI Dictionary

Penetrance

Penetrance is a percentage: [individuals having both a particular genotype and the phenotype expected from the genotype]/[individuals with the particular genotype] x 100.

For example, assume that red hair (b) is recessive to brown hair (B). Genotypes BB & Bb are expected to have brown hair, whereas genotype bb is expected to have red hair. There are 100 people with the bb genotype, but only 80 people have red hair. In this case, the penetrance is 80%.

Definitions in the literature

• Percentage of individuals with a particular genotype that express the phenotype expected of that genotype [1].