Define the term gene flow.

Hint: In humans, gene flow generally occurs through the actual migration, either voluntary or forced, of human populations.

Complete Answer:
- Gene flow, also referred to as gene migration, is the introduction from one population of one species to another of genetic material (by interbreeding), thus altering the composition of the gene pool of the receiving population.
- The introduction of new alleles through gene flow increases population diversity and allows possible new combinations of traits. While gene flow does not change allele frequencies for the species as a whole, it can alter allele frequencies in local populations.
- In the case of migration, the greater the gap in the allele frequency between residents and migrants and the greater the number of migrants, the greater the effect of migrants on the genetic make-up of the resident population.
- There are a number of factors affecting the rate of gene flow between different populations. Gene flow is predicted to be lower in species with low dispersal or mobility occurring in fragmented ecosystems where there are long distances between populations and limited population sizes.
- Mobility plays an important role in the migration rate, as highly mobile individuals tend to have greater migration prospects. When it comes to gene flow, bacteria are very interesting. In comparison to the other organisms like dogs and birds the bacteria are asexual.
- Bacteria and other asexual organisms sometimes, through alternative processes, transfer genetic variations. These processes, such as horizontal gene transfer, allow DNA to migrate between organisms without the need for sexual reproduction. In fact, much of the variation that occurs in life today has been caused by these gene transfers millions of years ago.

Note: Although migratory animals frequently bring new alleles from one population to another, they must interbreed with the new population for gene flow to occur.