Gene Flow

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).

Various factors influence the extent to which gene flow increases genetic variation:

1. Migration Rate: High migration rates result in more frequent exchanges of genetic material, intensifying the impact on genetic variation. Lower migration rates may still contribute to genetic diversity, but to a lesser extent.
2. Population Size: In larger populations, the potential for new alleles to persist and contribute to genetic diversity is more significant. In smaller populations, even low rates of gene flow can significantly impact genetic variation by changing the allele frequency of the gene.
3. Geographic Barriers: Permeable barriers, like land bridges, facilitate gene flow and increase genetic variation. Barriers that limit migration, such as oceans or mountains, can lead to population divergence and reduced gene flow.

Gene flow is a pervasive force in nature that is in action almost everywhere, from terrestrial to aquatic ecosystems.

Plant Pollination

In flowering plants, gene flow occurs through pollination. Bees, for instance, visit flowers to collect nectar, inadvertently transferring pollen between plants. This exchange of genetic material ensures the mixing of plant genes, contributing to the biodiversity of plant populations.

Insects and Wind Dispersal

Some butterfly species exhibit gene flow through wind dispersal during the larvae or pupae stage of their life cycle. This passive movement allows genetic material to be exchanged between geographically separated populations, influencing the genetic diversity within the species.

Migration in Birds

Arctic Terns are known for their annual migration from the Arctic to the Antarctic and back. They encounter individuals from different populations during these journeys, promoting gene flow. This movement helps maintain a degree of genetic homogeneity among widely dispersed populations.

Island Biogeography

Islands provide excellent examples of gene flow in action. Island populations often experience limited gene flow due to the surrounding water acting as a barrier. This isolation can lead to the development of unique species with distinct genetic traits. However, occasional migration events can introduce new genetic material, influencing the island’s biodiversity.

Human Populations

In human populations, migration patterns have shaped the genetic diversity observed today. For instance, the movement of humans out of Africa and their subsequent migration across the globe led to the development of diverse genetic traits in different populations. Modern transportation and globalization continue to influence gene flow among human populations.

Migration in Fishes

Salmon populations often migrate between freshwater and marine environments for breeding. Mixing individuals from different river systems during these migrations facilitates gene flow. This movement plays a crucial role in maintaining genetic diversity within salmon 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.

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.

Gene flow and genetic drift are two ingredients of variation in a population, causing genetic diversity. However, they differ in many ways, as listed below.