Difference Between Gene Flow and Genetic Drift

Main Difference – Gene Flow vs Genetic Drift

Gene flow and genetic drift are two processes that decrease the genetic variation within a population. However, both gene flow and genetic drift have longer term influences on evolution. The main difference between gene flow and genetic drift is that gene flow refers to the transfer of genes between populations whereas genetic drift is the variation of allele frequencies in small populations, allowing the disappearance of alleles from the population. Gene flow allows the combination of gene pools of two populations. However, gene flow allows the origination of new species by the gene transfer. Since genetic drift is a natural process, it is also called the random drift. Genetic drift occurs through founder effect and bottlenecks.        

Key Areas Covered

1. What is Gene Flow
      – Definition, Features, Role
2. What is Genetic Drift
      – Definition, Features, Role
3. What are the Similarities Between Gene Flow and Genetic Drift
      – Outline of Common Features
4. What is the Difference Between Gene Flow and Genetic Drift
      – Comparison of Key Differences

Key Terms: Antigenic Shift, Bottlenecks, Founder Effect, Gene Flow. Genetic Drift, Gene Migration, Gene Transfer, Horizontal Gene Transfer, Random Drift, Reassortment, Species

What is Gene Flow

The gene flow refers to the transfer of genes or alleles from one population to another population. The gene flow is also called gene migration. Gene flow into or out of a population affects the allele frequency of the population. The mobility of individuals is the major cause of gene flow from one population to another population. The greater the mobility of individuals, greater the gene flow. Animals are more mobile than plants. Seeds and pollen grains can be transported for great distances with the aid of wind and animals. Gene flow between two populations allows the populations to combine their gene pools with each other. This may reduce the genetic variation between the two populations. Therefore, gene flow reduces the tendency of speciation. This means gene flow repairs the developing differences, which may lead to producing a daughter species from the existing species. Physical barriers such as impassable mountain ranges, vast deserts, oceans, and man-made barriers may obstruct the gene flow.

Figure 1: Gene Flow

Gene flow can occur between species through hybridization or gene transfer as well. Gene transfer refers to the movement of genetic material across species. It includes horizontal gene transfer, reassortment, and antigenic shift. Both bacteria and viruses mainly undergo gene transfer. Horizontal gene transfer is the transfer of genetic material between unicellular organisms and/or multicellular organisms. Reassortment is the recombination of genetic material of different virus species through the chromosomal crossover.  In antigenic shift, two or more virus species combine and form a subtype with a mixture of surface antigens from each combined species. The gene flow is shown in figure 1. 

What is Genetic Drift

Genetic drift is the variation of the relative genotypic frequencies in a small population, allowing the disappearance of particular genes due to the death of individuals or incapability to reproduce. Genetic drift is also called random drift since it is a natural process. Genetic drift can occur in two ways: founder effect and bottlenecks. The recurrence of small population sizes causes the founder effect. A severe reduction of the size of a population is called bottlenecks. Since a new population starts from a small number of individuals, alleles or genotypes of the new population become fixed. Therefore, inbreeding coefficient as well as homozygosity of the population increase as a result of allele fixation. The genetic drift can be seen in populations that undergo regular extinction followed by the recolonization. The effective population size (N_e) determines the magnitude of the genetic drift. The N_e can also be defined as the number of inbreeding individuals in a population. N_e is used to calculate the amount of genetic drift expected in a particular population. The chance of an allele to be fixed in a population depends on N_e and the frequency of distribution of that particular allele within the population. If the frequency of a particular allele is low in a population, the chance of that allele disappearing from that population is high. Only the alleles with high frequencies within a population are fixed through genetic drift. This shows that genetic drift is involved in reducing the genetic diversity of the population.

Figure 2: Genetic Drift

However, genetic drift has long term evolutionary consequences. Accumulation of non-adaptive mutations facilitates the population subdivision or speciation. On the other hand, once the allele fixation occurs in different populations independently, the likelihood of mating between different populations of the same species can be reduced. This allows the emergence of new species. The genetic drift in a rabbit population is shown in figure 2. 

Similarities Between Gene Flow and Genetic Drift

• Both gene flow and genetic drift are involved in reducing the genetic diversity within a population.
• However, both gene flow and genetic drift have long term influences on evolution as well through speciation.

Difference Between Gene Flow and Genetic Drift

Definition

Gene Flow: Gene flow refers to the transfer of genes or alleles from one population to another population.

Genetic Drift: Genetic drift refers to the variation of the relative genotypic frequencies in a small population, allowing the disappearance of particular genes due to death of individuals or incapability to reproduce.

Correlation

Gene Flow: Gene flow allows the alleles to move from one population to the other.

Genetic Drift: Genetic drift is the changes in allele frequencies in a small population.

Works on

Gene Flow: Gene flow works on more than one populations at once.

Genetic Drift: Genetic drift works on small populations.

Contribution to Speciation

Gene Flow: Gene transfer, which is a process of gene flow between species, allows the origination of new species.

Genetic Drift: The accumulation of non-adaptive mutations and allele fixation facilitates speciation.

Examples

Gene Flow: The transportation of pollen for large distances and the mating of Europeans and native Americans, which results in offspring with mixed features are examples of gene flow.

Genetic Drift: The random deaths of green beetles, leaving brown beetles alive is an example of genetic drift.

Conclusion

Gene flow and genetic drift are two events that reduce the genetic diversity of a population. Gene flow is the transfer of genes from one population to the other. Gene transfer is the gene flow between two different species. Gene transfer allows the emergence of a new species. Genetic drift is the variation of allele frequencies of a small population. Genetic drift allows alleles with high frequencies to become prominent within a population. The main difference between gene flow and genetic drift is the effect of each event on the alleles of a population.

Reference:

1. Rodriguez, Tommy. “Gene Flow.” Darwin was Right. N.p., n.d. Web. Available here. 30 July 2017. 
2. “Genetic Drift.” APSnet. N.p., n.d. Web. Available here. 31 July 2017. 

Image Courtesy:

1. “Genetic drift in a population Figure 19 02 02” By OpenStax, Rice University – Textbook content produced by OpenStax, Rice University. (CC BY 4.0)  via Commons Wikimedia
2. “Gene flow” By Tsaneda – Gene_flow.jpg at wikieducator (CC BY 3.0) via Commons Wikimedia