An indicator of the phenotypic manifestation of an allele in a population, expressed in the frequency of manifestation of a certain gene in individuals of a related group that have the corresponding genotype. The probability of phenotypic manifestation of a gene is expressed as a percentage (for example, the ratio of sick individuals to the number of carriers of the corresponding gene). Examples: congenital hip dislocation – penetrance 25%; gout (joint disease) – penetrance in men 20%, in women 0%; Otosclerosis (defect of the middle ear ossicles) – penetrance of 30%. They depend on endogenous and exogenous factors.