Gene flow is the exchange of genes between populations as a result of the dispersal of gametes or zygotes . It involves the spread of new gene variants among different populations through dispersal. Gene flow and mutation are, therefore, the only means by which new genetic factors may be introduced into a population. To understand how gene flow affects gene frequencies in populations, biologists have developed a number of models representing different possibilities. In real populations, the processes of gene flow are much more complex than this.
Nature can be difficult to model.
In the wild, individuals are more likely to mate with neighbors. Thus, the concept of panmixia is an abstraction. Migrating individuals are more likely to come from nearby populations. Populations can be spread out in two dimensions over an area of land or strung like beads in one dimension along a river bank. Alternatively, there may be one large population with an internal genetic structure resulting from a tendency for individuals to mate with others born in the same region.