Also referred to as gene migration, gene flow is the introduction of genes from one population to the gene pool of another population. This process changes the composition of the gene pool of the receiving population. Good examples of gene flow include the movement of pollen grains from one plant to another and the movement of people from one place to another.
Gene flow also occurs without migration. For instance, when people travel to another area and mate with people in that area, transfers of genes occur within the population even if the travelers return home. If red-haired people travel from Scotland to another place and mate there, in the next generation there may be some individuals in this destination that possess that trait.
Gene flow also occurs between species. Segments of DNA are transferred from one species to another by viruses as they attack the cells of plants and animals. The introduction of alleles through gene flow allows for the combination of traits and increases variability within the receiving population. The amount of gene flow varies among organisms because sedentary organisms are more isolated than mobile organisms. Ideally, gene flow introduces new genes into a population consequently increasing the genetic variation of the population. Also, gene flow makes distant populations genetically similar.