Gene flow may change allele frequencies

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Few populations are completely isolated from other populations of the same species. Migration of individuals and movements of gametes (in pollen, for example) between populations—a phenomenon called *gene flow—can change allele frequencies in a population. If the arriving individuals survive and reproduce in their new location, they may add new alleles to the population’s gene pool, or they may change the frequencies of alleles present in the original population.

*connect the concepts If gene flow between two populations stops, those populations may diverge and become different species; see Key Concept 22.2.