Gene flow, also called gene migration is basically the transfer or movement of alleles or genes from one population to another. Gene flow can happen in different processes such as migration, environmental effects, vegetation, or even changes in weather in a certain area. When genes are transferred to a new place where those genes do not exist before, genetic variation can occur.
There are factors that affect the gene flow. First is the physical barrier which includes impassable geographical structures that prevent organisms from going to other areas. Physical barriers can be natural or artificial. Natural barriers are like that of mountain ranges or cliffs, large deserts or oceans. Example of artificial or man-made barrier is the Great Wall of China. The other factor is the female choice wherein females are not responding to the population in other areas thus making the gene of a certain population hindered.