Genetics and statistics: The basics

The penetrance of a particular genotype at a disease locus is the probability that individuals possessing that genotype will develop the disease. More rigorously, the pentrance of a genotype-phenotype pair is defined as the probability that an individual would have the phenotype given that they have the genotype. The penetrance of a disease is said to be incomplete (or partial, or reduced) if not all individuals possessing the disease genotype develop the trait. Such incomplete penetrances may be functions of many variables, including age, gender, environment, and the presence of certain alleles at other genetic loci.