n. the mating of individuals that are closely related. Inbreeding increases the risk of perpetuating certain genetic defects in the family, as in consanguineous marriages. Inbreeding within small populations, such as geographically isolated populations, leads to increased frequency of particular mutations within such groups. This fact has been used to demonstrate the founder effect for certain cancers and other disorders. Inbreeding studies have contributed to efforts to identify and test for mutations predisposing to disease in some groups of people. Compare outbreeding.