Natural selection, genetic drift, and gene flow may sound similar, but they are evolutionary processes, and they have several significant differences.
Genetic Drift
In the genetic drift, the frequency is changed within the population by the allele due to some sort of random sampling. As a result, the adaptations are not produced. Genetic drift is caused by the two mechanisms and the first mechanism is the bottle effect.
The Bottle Effect
The bottle effect is the genetic drift in the population after the happening of the catastrophic events, such as the floods. It happens due to the reduced allele frequency in the main trait, due to the death of various individuals carrying that allele. Most of the population cannot survive and they die and the random individuals are left behind as the survivors. The bottle effect describes the genetic drift due to traumatic events in the populations.
The Founder Effect
The second mechanism of genetic drift is known as the founder effect. It happens when some members of the population are broken away, and they create their group. By the creation of a new group due to the random sampling, the allelic frequency can be dramatically shifted depending on the selective pressure that is placed on the individuals. The founder effect may feel like pretty same to the bottle effect.
Gene Flow
There is a significant difference between the gene flow and the genetic drift, as gene flow causes the transfer of gametes or alleles from one population to another one. Generally, it happens due to the migration of the population, or when a population becomes geographically isolated. It is quite a rare process. Gene flow occurs due to the exchange of genes by the mixing of the populations. It is the movement of the genes, in or out of the population. Various factors affect the rate of gene flow, between the various populations. Mobility has a significant role in the migration rate. Allopatric speciation and the sympatric speciation may cause barriers for the gene flow.
Genetic Variation due to Gene Flow
Gene flow causes the genetic variation, due to which the organisms differ from each other. It is an important mechanism to transfer the genetic diversity among the populations. In some cases, the migration may cause the addition of the novel genetic variation to the gene pool of a population or the species. Gene flow can also occur between the species, by the hybridization, and the horizontal gene transfer.