Which mechanism describes changes in allele frequencies due to random chance?

The mechanism that describes changes in allele frequencies due to random chance is genetic drift. This phenomenon occurs particularly in small populations, where random events can significantly influence which alleles are passed on to the next generation. For instance, if a natural disaster randomly eliminates a portion of the population, the frequencies of alleles in the surviving group may differ from those in the original population purely by chance, not because of any advantage or disadvantage of particular alleles.

In contrast, natural selection involves changes in allele frequencies driven by the advantageous traits that enhance survival and reproduction. Gene flow refers to the transfer of alleles between populations through migration, which tends to increase genetic variation within populations. Mutation introduces new genetic variations into a population's gene pool but does not inherently lead to changes in allele frequencies due to random chance like genetic drift does.