Final answer:
The process by which chance events alter gene frequencies within a population is known as genetic drift. It is a random process that can cause changes in allele frequencies, especially within small or isolated populations.
Step-by-step explanation:
The process of chance assuming a preeminent role in altering gene frequencies within a population is known as genetic drift. This phenomenon can occur due to random events that cause certain alleles to increase in frequency by chance alone. For example, in a phenomenon known as the founder effect, a small group from a larger population may become isolated, and their gene pool may not reflect that of the original population. Whatever alleles they carry will establish the genetic basis of the new population. Genetic drift can also occur in large populations but is more pronounced in small ones. While natural selection is a non-random process where traits that confer a survival advantage become more common in a population, genetic drift lacks such systematic direction and changes allele frequencies purely by chance.