The change in allele frequencies that occur due to the colonization of a new location by a small group of individuals is called

Founder effect.

Explanation:

The founder effect is a case of genetic drift in which a small population sample of a limited number of individuals is shed from a larger population, its gene pool carrying only a part of the genetic diversity represented in the source population. Thus, it is likely that the genetic destinies of the population of origin and of the new population are established in different ways. When a new generation has randomly distributed alleles, with a large enough sample size, we can expect that the gene pool of the new generation will more or less represent the gene pool of the previous generation.