Genetic Drift and Gene FlowNatural selection is not always necessary for genetic change to occur. Gene pools can change in the absence of natural selection. Two processes that cause the gene pools to change are genetic drift and gene flow.

Genetic Drift

There is typically a good range of diversity of traits within a population but any given trait might only exist in the DNA of a limited number of individuals. If those individuals reproduce more or less successfully by sheer happenstance, then we get genetic drift. Those alleles become suddenly more or less prominent in the gene pool.

The bottleneck effect occurs when a population goes through a traumatic event where a random majority of the population doesn’t make it. The surviving population no longer represents the gene pool of the original population. Certain traits are more common while some other traits are eliminated.

The founder effect describes genetic drift that occurs when a few members of the population break away from the pack and “found” their own population. Because a small number of individuals start a new population, the trait frequency in this new gene pool can be dramatically altered.

Bottleneck effect

Gene flow

Gene flow is the process of individuals moving in and out of a population causing a change in the population’s gene pool. Gene flow either eliminates or introduces new traits to the population’s gene pool.

Gene flow can reduce the genetic differences between populations, and thus act against evolution.