Genetic Drift

    Let's go over genetic drift!

    First and foremost, genetic drift is a random process that causes allele frequencies to change in a population over time. Genetic drift can significantly reduce genetic variation and increase the frequency of once rare alleles. Drift will also increase the chance that the allele goes into fixation. Drift is more likely to occur in smaller populations since it would be less likely that a certain allele would be lost in a larger population.

    In a rabbit population, the B and b alleles determine fur color. For this rabbit population, something random happens that causes the rabbits to completely lose the b allele, which causes the B allele to go to fixation. It is important to note that genetic drift does not care about how beneficial or harmful an allele is to a population- it is not based on selection and is not a mechanism of adaptation.

Two types of genetic drift are the bottleneck effect and founder effect! While these two different types of drift are similar in their outcome and lead to a loss of genetic variation, they occur in different ways.

    In the bottleneck effect, a random event will reduce the population size and the genetic variation is lost or reduced. This can be during a natural disaster or any random process in which the majority of a population is killed so the allele frequencies of the surviving population is different and less diverse than that of the original population. In the case of the northern elephant seal, hunting reduced their population levels which significantly reduced genetic variation. 

    In the founder effect, a subset of a population goes on to find a new population which will have reduced genetic variation and different allele frequencies. Darwin’s finches are an example of the founder effect in which species from a small subset of finch populations contributed to their subset populations, reducing the overall population genetic variation. Darwin’s finches also have different phenotypes due to the isolation of the subpopulations.