What is the effect of migration on genetic variation between populations?

Migration, or gene flow, occurs when individuals from one population move to another population, introducing new genetic material. This process generally leads to an increase in genetic variation within the receiving population because it brings in different alleles. However, in the context of comparing genetic variation between two distinct populations, migration can result in a reduction of genetic differences between those populations.

When a population experiences migration from another, particularly if one population is migrated to the other frequently, the two populations become more genetically similar over time. Thus, the unique genetic traits that may have developed separately in each population can be blended together, decreasing the overall genetic divergence.

In situations where populations are geographically or reproductively isolated, migration can diminish the distinct genetic identities that have developed over time. Therefore, while migration enriches the genetic diversity within a specific population, it simultaneously decreases genetic variation between the two populations that are exchanging individuals.