1. The problem asks: What occurs when allele frequencies change due to migration of a subgroup of a population? 2. This is a question about population genetics, specifically how allele frequencies can change in a population. 3. The key terms are: - Bottleneck effect: a sharp reduction in population size leading to loss of genetic variation. - Natural selection: differential survival and reproduction of individuals. - Founder effect: when a new population is established by a small number of individuals, causing allele frequencies to differ from the original population. - Genetic drift: random changes in allele frequencies, especially in small populations. 4. Migration of a subgroup introduces new alleles or changes allele frequencies in the population due to movement of individuals. 5. The correct term for allele frequency change due to migration is "gene flow," but among the options, the closest is the founder effect, which involves a subgroup establishing a new population with different allele frequencies. 6. Therefore, the answer is: The founder effect.