Genotype is the hereditary makeup of an individual. Mutations are changes in the genetic material. Random genetic drift refers to a change in gene frequencies that is completely random, i.e., there is no necessary selection for or against a particular allele. The allele simply occurs, by chance alone, more or less often in a generation than in the previous generation. In order for this drifting to influence the entire population s genotype frequency, it is necessary to have a small population.
Migration refers to the flow of genes into or out of an isolated population through inbreeding.
A small amount of gene flow often occurs between populations that normally do not interbreed. As with mutation and random genetic drift, migrants carrying different alleles into or out of a population have a much better chance of changing the population s gene frequencies if the population is small. Founder effect occurs when a small group of individuals forms a new population, which is isolated from the original population. The gene frequencies of subsequent generations may be very different from the original population simply because the small number of individuals who are founders probably do not carry all the allelic forms found in the original population. In this activity, beans of two different colors demonstrate evolutionary forces, plus the effects of population size on these forces.