Achange in the gene pool of a population due to chance is
gene flow
genetic drift
a mutation
genetic diversity

Genetic drift

Explanation:

Shifts from generation to generation within the same gene pool are called micro evolution.

Due to gene flow,natural selection, mutation, and  genetic drift,  Allele frequencies in population may shift. These are recognized as four fundamental powers of evolution

Because of random chance, there is genetic diversity in that population's allele levels in genetic drift. A small population would thus allow for a greater chance of sampling error and a shift in allele frequencies would result in a misrepresentation of gene pool of the parent generations.The evolutionary process is mischaracterization of allele frequencies that cause population change.