Migration into or out of a population may be responsible for a marked change in gene pool frequencies (the number of individual members with a particular trait). Immigration may result in the addition of new genetic material to the established gene pool of a particular species or population, and conversely emigration results in the removal of genetic material.
There are a number of factors that affect the rate of gene flow between different populations. One of the most significant factors is mobility, and animals tend to be more mobile than plants. Greater mobility of an individual tends to give it greater migratory potential.
Barriers to gene flow
Physical barriers to gene flow are usually, but not always, natural. They may include impassable mountain ranges or vast deserts, or something so simple as the Great Wall of China, which has hindered the natural flow of plant genes  . Examples of the same species which grow on either side have been shown to be genetically different.
Gene flow in humans
Gene flow has been observed in humans, for example in the United States, where a white European population and a black West African population were recently brought together. The Duffy blood group gives carriers some resistance to malaria, and as a result in West Africa, where malaria is prevalent, the Fyo allele is essentially one hundred percent. In Europe, which has much lower levels of malaria, have either allele Fya or Fyb. By measuring the frequencies, the rate of gene flow (i.e. interracial breeding) between the two populations can be measured. Gene flow is greater in the North than in the South, due to cultural attitudes.
Gene flow between species
Genes can flow between species, as when bacterial DNA is transferred to animals or plants.
Models of gene flow
- Su, H et al. The Great Wall of China: a physical barrier to gene flow?. Heredity, 90, 212 - 219, (2003).
|Basic topics in evolutionary biology|
|Processes of evolution: macroevolution - microevolution - speciation|
|Mechanisms: selection - genetic drift - gene flow - mutation|
|History: Charles Darwin - The Origin of Species - modern evolutionary synthesis|
|Subfields: population genetics - ecological genetics - molecular evolution - phylogenetics - systematics - evo-devo|
|List of evolutionary biology topics | Timeline of evolution|