the occurrence of a gene at increased frequency in a group or colony that was initially established by a small number of members of a larger population. The limited number of founders results in limited genetic diversity and a nonrandom genetic sample of the original population. The presence of a founder effect leads to a characteristic genetic makeup, which can allow the tracing of the migration of a particular ethnic group or population over time. Its presence is also associated with the predisposition of some groups to certain diseases. A founder effect has been identified for mutations predisposing to breast cancer among Eastern European Jews, for example.