Genetic Drift and Founder Effect

Genetic Drift Genetic drift causes rapid random changes in gene pool frequencies occurring in small populations. The smaller the population is the more susceptible they are to genetic drift. In small populations that are isolated from other populations, significant changes in gene frequencies can occur by chance. Genetic drift is totally independent of mutation, recombination, and natural selection.

Example of Genetic Drift Rapid genetic drift over three generations

Founder Effect “The overrepresentation of a specific allele at one or more loci in a new population that arises from a small number of individuals whose small gene pool may be unrepresentative of the parental population initially or as a result of the ensuing genetic drift” The founder effect occurs when a genetic trait is introduced to a small population and is passed on through the generations This occurs when there is a small ancestral or founding population. The potentially numerous descendants of the founders often have similar genetic makeup. This explains why rare diseases are more frequent among descendants of people who had them.

Geneticists, who have studied the Amish’s culture (in eastern Pennsylvania) for decades have found that because of their closed population stemming from a small number of German immigrants -- about 200 individuals -- the Amish carry unusual concentrations of gene mutations that cause a number of otherwise rare inherited disorders, including forms of dwarfism. Example of mutation from founder effect