What term describes random changes in allele frequency that can lead to fixation of only one allele?

The term that describes random changes in allele frequency that can lead to the fixation of only one allele is genetic drift. Genetic drift is a process that occurs in small populations where chance events can cause certain alleles to become more or less common purely by random sampling of alleles. Over time, this can result in the fixation of one allele, meaning that it becomes the only allele present in that population, while other alleles may be lost completely.

This random change in allele frequency can have significant impacts on the genetic diversity of a population and is particularly crucial in understanding evolution. Unlike natural selection, which involves differential survival based on advantageous traits, genetic drift is non-directional and does not necessarily favor alleles that provide any survival advantage.

In contrast, mutation introduces new genetic variants, selection favors certain traits that provide an advantage, and migration involves the movement of individuals between populations which can alter allele frequencies but is not solely based on chance. Each of these processes plays a role in shaping the genetic landscape of populations, but genetic drift specifically emphasizes random changes leading to the fixation of alleles.