Answer and Explanation:
The founder effect is a special case of genetic drift.
The Founder effect refers to the consequences that occur from the origin of a new population produced by a small number of founder individuals that come from an ancestral bigger population. The new population originated from a few founder individuals, who came from a bigger population and that established in a new environment.
This small population might or might not be genetically representative of the original one. It might show poor genetic variation and hence, a high possibility of expressing a peculiar allelic composition. Some rare alleles might be in exceed or might be completely lost. Consequently, when the small population increases in size, it will have a genetically different composition from the original one. In these situations, genetic variability is reduced and there is a high possibility of developing a peculiar allelic composition. If the number of individuals that originates the new population is very low, the founder effect will be very extreme, because the magnitude of this change is inversely related to the original number of the founder individuals. These changes produced by genetic drift accumulate in time, and eventually, some alleles get lost, while some other might set.
There are certain examples of the founder effect, such as Huntington's disease in South Africa or the Ellis syndrome characteristic of the Amish people from Pennsylvania.
