Founder effect

The founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals drawn from a larger source population, a concept Ernst Mayr formally described in 1942. Because a small founding group is unlikely to be genetically representative of the population it came from, it carries only a fraction of the original genetic diversity, and the new population then experiences stronger genetic drift, more inbreeding and reduced genetic variation, so that some genes can disappear entirely by chance while others become unusually common. French Canadians in Quebec illustrate the effect: about 8,500 French settlers arrived between 1608 and 1760, immigration from France largely stopped after the British takeover of 1760, and the descendants' high fertility and limited intermarriage mean the genetic contribution of the original founders still accounts for roughly 90 percent of the regional gene pool today, despite some later admixture from other groups.