Final answer:
The random change in allele frequency by chance is known as genetic drift, which can cause significant changes in a population's genome without any conferred advantage.
Step-by-step explanation:
The random change in allele frequency over time that is brought about by chance alone is known as genetic drift. This phenomenon occurs when, by chance, some individuals have more offspring than others, and not due to an advantage conferred by some genetically-encoded trait. For example, it could happen just because one male was in the right place at the right time. Genetic drift can lead to significant changes in a population's genome, often in conjunction with other evolutionary forces like natural selection and can cause alleles to become more or less prevalent in the population at random.