What does the Founder Effect refer to in population genetics?

The Founder Effect refers specifically to the phenomenon where a small group from a larger population establishes a new population in a different location. This small group may not represent the genetic diversity of the original population, which can lead to reduced genetic variation in the new population. Because only a subset of the original population contributes to the gene pool of the new population, certain alleles may become more or less common purely by chance, affecting the genetic structure of the new group.

In contrast, the other options address different concepts in population genetics. A geographic barrier that prevents gene flow relates to allopatric speciation but does not specifically highlight the role of a small group founding a new population. A selection pressure that reduces genetic diversity concerns the impacts of environmental factors or competition, which may lead to selective sweeps rather than the establishment of a population. An increase in genetic variation within a population stands in direct contrast to the Founder Effect, as this effect often leads to decreased variation due to the limited genetic contributions from the founders.