Gene Flow is the movement of genes and alleles between populations. It can occur through the migration of, or their gametes, and can be seen in both animals and plants. It is important to note that gene flow only occurs when a gene or allele enters a receiving population's gene pool. This can have a significant effect on the evolution and genetics of a population.

Gene flow can vary between two populations. For example, plants pollinated by birds or bats will their gametes further away than wind-pollinated plants, and animals like frogs will have a lower rate of gene flow than more mobile organisms like birds. When there is a significant rate of gene flow between two populations, they can eventually share the same gene pool, which tends to homogenize the genetic makeup of populations.

A trait or allele that is beneficial in one population may not necessarily have the same effect in the receiving population. This is because the introduction or reintroduction of a trait to a population through gene flow is considered a random event in population genetics. An example of this is the water snake, Nerodia sipedon, which inhabits the area of Lake Erie in Ohio and Ontario. The species is divided into several subpopulations that differ in their coloration. Most snakes on the mainland have a strong band pattern, which is advantageous for camouflage in marshes. On the other hand, most snakes that reside on the islands in the lake have a uniform coloration that is more advantageous along rocky shores. Despite this, a small fraction of snakes with bands are still found on these islands. This is because about 3-10 snakes are estimated to migrate to the islands per year, reintroducing the alleles for the band pattern into the islands.

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flow is a fascinating process that can have significant effects on the evolution and genetics of populations. When gene flow occurs between populations of the same species (intraspecifically) or between populations of different species (interspecifically), it can lead to the movement of genes and alleles. Based on the water snake example, we can see that gene flow from the mainland tends to homogenize the genetic diversity of these populations and tends to make them more similar. However, in cases where the introduced allele is disadvantageous in the rocky environment of the receiving population, their frequency does not increase due to natural selection.

On the other hand, gene flow can also lead to beneficial adaptations in populations. An example of this is the acquisition of insecticide resistance in Anopheles coluzzii, the African malaria mosquito. The insecticide resistance allele arose as a new mutation in another mosquito, A. gambiae. This mutation rapidly increased in frequency in several subpopulations of A. gambiae, due to its strong selective advantage for these mosquitoes exposed to the insecticide. The allele eventually entered the gene pool of A. coluzzi through interspecific gene flow with A. gambiae, in an area where both species are present. The allele then spreads to other subpopulations of A. coluzzi through intraspecific gene flow.

It is important to note that gene flow between species is only possible in young species that still reproduce in areas where both species live. In these areas, they produce species hybrids mate of the parent species, introducing the allele to the gene pool of that species.

Overall, gene flow is a complex process that can have significant effects on the evolution and genetics of populations. It can lead to both homogenization and beneficial adaptations, depending on the environmental conditions and the introduced alleles.

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Gene flow is a powerful mechanism that can lead to significant changes in allele frequencies in a population, driving evolution alongside genetic drift and natural selection. However, these changes beneficial receiving or advantageous.

In some cases, gene flow can lead to the introduction of genes or alleles that are disadvantageous to the receiving population, as we saw in the water snake example. In contrast, genetic drift is caused by random shifts in allele frequencies from one generation to the next, and it tends to reduce genetic diversity within a population and increase differences between populations.

Despite their differences, both gene flow and genetic drift are mechanisms that drive evolution, and both can have significant effects on the genetics of populations. For example, the human evolution story is an example of gene flow between species, such as the acquisition of the gene related to human diabetes from Neanderthals. These events of gene flow between species were not rare, and they have contributed to the genetic diversity of the human population we see today.

In summary, gene flow is a crucial mechanism that can cause evolution by producing changes to the allele frequencies in populations. Although it is random like genetic drift, gene flow can lead to beneficial adaptations, and it can increase the genetic diversity within a population, while reducing differences between populations.

Gene Flow - Key takeaways Gene flow is one of the main mechanisms driving evolution, genetic drift, and natural selection. Gene flow occurs between populations of the same species (intraspecific) or between populations of different species (interspecific).The level of gene flow between populations depends on the mobility or dispersal capabilities of adult individuals or their gametes to reach another population. A disadvantageous allele can be maintained in a population if it is continuously being reintroduced through gene flow. Gene flow can counteract the effects of natural selection and genetic drift. It increases the genetic variation in a population (through the introduction of new alleles) and decreases the genetic differences between populations (by sharing alleles). When gene flow is reduced or stopped, each population adapts to local conditions, and their gene pool keeps diverging, eventually leading to speciation.

References

1. Anna Tigano and Vicky Friesen, Genomics of local adaptation with gene flow, Molecular Ecology, 2016.

2. Campbell et al., Biology 7th edition, 2020.

3. Huerta-Sánchez et al., Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA, Nature, 2014.

4. The deep roots of diabetes, Understanding Evolution, 2014. (https://evolution.berkeley.edu/evo-news/the-deep-roots-of-diabetes/)

Gene Flow

What is gene flow?

Gene flow refers to the movement (in and out) of genes and alleles caused by the dispersal of organisms, or their gametes, between populations. 

What are gene flow and genetic drift?

Both gene flow and genetic drift are evolutionary mechanisms (along with natural selection), they can produce changes in an allele frequency. However, gene flow can counteract the effects of the other two, as it tends to increase the genetic variation in a population and decrease the genetic differences between populations.

What is an example of gene flow?

An example of gene flow is the acquisition of insecticide resistance in Anopheles coluzzii, the African malaria mosquito. The resistance allele arose as a new mutation in another mosquito, Anopheles gambiae, and then entered A. coluzzi’s gene pool through gene flow between the two species.

Does gene flow increase genetic variation?

Yes, gene flow can increase genetic variation if it introduces new alleles in the receiving population.

What causes gene flow?

Gene flow is caused by individuals breeding with individuals from different populations. This implies the movement (migration or dispersal) of adult individuals or their gametes from one population to another.

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