What is Gene Flow?
Gene flows also called migration is any movement of individuals, and/or the genetic material they carry, from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries.
If genetic variants are carried to a population where they previously did not exist, gene flow can be an important source of genetic variation. In the graphic below, a beetle carries the gene version for brown coloration from one population to another.
The genetic variation in modern human populations has been critically shaped by gene flow. For example, by sequencing ancient DNA, researchers have reconstructed the entire Neanderthal genome and they’ve found that many snippets of these archaic sequences live on in modern humans.
It’s clear that ancient humans and Neanderthals interbred, and that this gene flow introduced new genetic variation to the human population. Furthermore, this ancient gene flow seems to affect who we are today.
Neanderthal gene versions have been linked to immune functions, metabolic functions (e.g., affecting one’s risk of developing diabetes), and even skin color.
When Causes Gene Flow
Gene flow is the movement of genes into or out of a population. Such movement may be due to migration of individual organisms that reproduce in their new populations, or to the movement of gametes (e.g., as a consequence of pollen transfer among plants).
In the absence of natural selection and genetic drift, gene flow leads to genetic homogeneity among demes within a metapopulation, such that, for a given locus, allele frequencies will reach equilibrium values equal to the average frequencies across the metapopulation.
It is accomplished through the movement of individuals between two populations of the same species. This movement can be facilitated by migration, where individuals physically relocate, or by transferring gametes (sperm and egg cells) between populations during sexual reproduction.
As individuals from different populations interbreed, they exchange genetic material, influencing the genetic composition of both populations.
Alternatively, it can occur between two species, from bacteria or viruses to higher organisms, through horizontal or lateral gene transfer (HGT or LGT).
Factors Affecting Gene Flow
There are a number of factors that affect the rate of gene flow between different populations. Gene flow is expected to be lower in species that have low dispersal or mobility, that occur in fragmented habitats, where there are long distances between populations, and when there are small population sizes.
Mobility plays an important role in dispersal rate, as highly mobile individuals tend to have greater movement prospects. Although animals are thought to be more mobile than plants, pollen and seeds may be carried great distances by animals, water or wind.
When gene flow is impeded, there can be an increase in inbreeding, measured by the inbreeding coefficient (F) within a population. For example, many island populations have low rates of gene flow due to geographic isolation and small population sizes.
The Black Footed Rock Wallaby has several inbred populations that live on various islands off the coast of Australia. The population is so strongly isolated that lack of gene flow has led to high rates of inbreeding.
Examples of Gene Flow in Nature
Gene flow is the exchange of genes between two separate populations. This is most often accomplished when animals or spores from plants migrate to a new area.
Any time a gene is introduced into a population where that gene once did not exist, gene flow has occurred. Discover some gene flow examples in both the plant and animal kingdoms.
Examples of Gene Flow for Plants
Gene flow can occur among plants in a wide variety of ways.
- Pollinators from a population of flowers on one side of a river transport pollen to the flowers on the other side of the river, producing floral offspring.
- Pollen from trees is blown far, far away to a completely separate group of trees and pollinates their flowers, producing trees with genetic characteristics of each population.
- Seeds and pollen from conifers on one side of a gulch are blown high into the air, eventually reaching and pollinating trees on the other side of the gulch.
- Fruit in the cucurbit family (cucumbers and most squash) must be pollinated by bees. If a bee carries pollen from one variety of squash or cucumber to another (within the same species), that will result in hybridization.
- If you save seeds from a squash or cucumber plant and the resulting fruit does not look like the fruit from the original plant, that is the result of gene flow.
- A farmer that wants to produce a particularly gene resistant variety of tomato, corn or other crops will use gene flow to cross plants together based on specific characteristics. This is called hybridization.
- Modern grains, like the durum wheat that is used to make bread, pasta and other flour-based food products, were developed through a hybridization process.
- Lager beer yeast (Saccharomyces pastorianus) is the result of gene flow (hybridization) between two other types of yeast, one of which has a higher level of cold tolerance than the other. The hybrid variety is more well-suited to fermentation than the original types.
- When people deliberately bring in plants that are non-native, they can end up starting the gene flow process that allows invasive species to evolve. Gene flow will occur between new plants and existing ones, often strengthening existing plants so they become harder to control or creating hybrids that become invasive.
- As the strongest genes survive and cross, species that are resistant to herbicide can develop. When this occurs, it can be difficult (or impossible) to curb the spread of unwanted plants, such as weeds.
- When the plants that grow back on previously damaged land through secondary succession are different from what was originally there, the change can be a result of gene flow.
Gene Flow Examples for Animals
There are many gene flow examples in the animal kingdom.
- Blue-eyed people from Sweden move to a small town in Mexico where people all have brown eyes. When they mate, some of their children now have blue eyes.
- Some birds with shorter beaks enter into a population of birds with much longer beaks, resulting in the hatching of birds with medium-sized beaks.
- A Maine coon cat is brought to an island where only wild tabby cats live. After mating with other cats on the island, some of the kittens have bushy tails and tufted ears.
- A bunch of women from West Africa, where malaria is present, mate with a group of Europeans. Their children are less susceptible to contracting malaria due to the presence of antibodies from their West African mothers.
- Rhinos from one herd move to a new area and breed with rhinos of a completely different herd.
- A man with very dark skin moves to a remote village in Eastern Europe, where most people have light skin. Their children and grandchildren show evidence of this genetic flow when some are born with dark skin.
- Several red foxes move into and mate with a silver fox population.
- Two lion prides meet in the Savannah and end up procreating, introducing genetic diversity to each tribe.
- Red parrots are brought on an expedition to a remote section of the jungle with only blue parrots, introducing color variation into the gene pool of jungle parrots.
- Brown beetles enter into a community consisting solely of green beetles, creating offspring with greater color diversity.
- Interbreeding occurs due to the migration of tall members of an African tribe to an area of South America where people are much shorter, making possible new combinations of genetic traits, including variations of skin color and height.
- A population of moths with a high frequency of white alleles enters a population of darker-colored moths. Over time, more and more white moths are born as a result.
- Tigers with enhanced sensitivity in the dark mate with a group of tigers with less sensitive eyes, allowing a greater population of tigers with enhanced eyesight to be born after a few generations.
Effect of Gene Flow on Population
Gene flow within a population can increase the genetic variation of the population, whereas gene flow between genetically distant populations can reduce the genetic difference between the populations. Because gene flow can be facilitated by physical proximity of the populations, gene flow can be restricted by physical barriers separating the populations.
Gene flow is found to increase genetic variation in a population. It acts as the raw material on which genetic variation occurs. It works principally through:
1. Introduction of New Genes
As individuals migrate and interbreed between populations, they bring new alleles that are absent or less frequent in the recipient population. It causes an increase in genetic variation within the population by expanding the pool of available alleles.
2. Recombination and Mixing of Genes
During interbreeding, the recombination of genetic material occurs, leading to the formation of new combinations of alleles in offspring.
3. Maintenance of Variation
Gene flow counteracts genetic drift and natural selection, which can reduce genetic diversity over time.
Importance of Gene Flow in Nature
As we know, gene flow acts as one of the raw materials of evolution by maintaining biodiversity. It helps in:
Creating Biodiversity in Population
The primary role of gene flow lies in its capacity to mold and maintain genetic diversity. As organisms migrate and interbreed, genetic material flows seamlessly.
This constant mingling mitigates the effects of genetic drift and counteracts the selective pressures that could lead to uniformity. In essence, gene flow acts as a genetic bridge, connecting populations and fostering a shared genetic reservoir.
Mitigating Genetic Drift
Genetic drift, the random change of allele frequencies in a small population, can lead to the fixation or loss of specific alleles over time. Gene flow acts as a counterforce, infusing genetic material and preventing the fixation of alleles by introducing new variations.
This continuous influx of diversity maintains the adaptive potential of populations, ensuring they remain resilient in the face of environmental challenges.
Improving Adaptation in Population
Gene flow is not merely a passive force. It actively contributes to the adaptive capabilities of populations. By introducing new genetic material, populations access a broader pool of traits.
This influx of variation provides the raw material for natural selection to act upon, enabling populations to adapt to changing environmental conditions.