What phenomenon describes a change in allele frequency due to random chance?

The phenomenon that describes a change in allele frequency due to random chance is genetic drift. Genetic drift refers to the random fluctuations in the frequencies of alleles within a population, particularly in small populations where chance events can significantly influence which alleles are passed on to the next generation. For instance, if a natural disaster randomly eliminates a portion of a population, the surviving individuals may not have a representative sample of the original genetic diversity, leading to a shift in allele frequencies.

In contrast, natural selection is a process where certain traits become more common in a population because they confer some advantage for survival and reproduction. Gene flow involves the transfer of alleles or genes from one population to another, which can introduce new genetic material into a population and alter allele frequencies. Mutation is a direct alteration of the DNA sequence that can create new alleles but does not primarily operate through random chance in the way that genetic drift does. Each of these processes plays a role in evolution, but it is genetic drift that specifically highlights the impact of random events on allele frequencies.