Penetrance

The proportion of individuals in a population that express the phenotype expected from their genotype with respect to a specific gene. Measures the extent to which phenotype predicts genotype.

The probability of a gene or genetic trait being expressed. "Complete" penetrance means the gene or genes for a trait are expressed in all the population who have the genes. "Incomplete" penetrance means the genetic trait is expressed in only part of the population. The percent penetrance also may change with the age range of the population.