Gene Flow and Genetic Drift

Hey All AIPMT Biology Aspirants, learn about Gene Flow and Genetic drift, which are the two major evolutionary processes, out of four.

GENE FLOW:  It’s simply the flow/movement of genes from one population to other.

  • Gene flow occurs when individuals leave one population, join another, and breed.
  • Transfer of alleles into or out of a population occurs due to the movement of fertile individuals or their gametes.
  • Frequency of alleles changes when gene flow occurs, because arriving individuals introduce new alleles to new population, while departing individuals remove alleles from their source population.
  • New genes/alleles are added to the new population and these are lost from the old population.
  • It is an important agent of evolutionary change.
  • Emigration from a source population removes alleles from this population. Immigration to a new population adds new alleles to this new population. So, emigration and immigration results in gene flow.
  • It equalizes allele frequencies between the source population and the recipient population.

GENETIC DRIFT: If the change in allele frequencies occurs randomly or by chance, it is called by genetic drift.

  • Genetic drift can cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations.
  • Sometimes the change in allele frequency is so different in the new sample of population that they become a different species.
  • It is significant in small populations.
  • It can cause allele frequencies to change at random.
  • It can lead to a loss of genetic variation within populations.
  • It can cause harmful alleles to become fixed.
  • It may cause those alleles to increase in frequency that decrease fitness.

Certain circumstances can result in genetic drift having a significant impact on a population. Two examples are the Founder effect and the Bottleneck effect.

The Founder Effect: When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool differs from the source population; this is
called as founder effect. And the isolated population is called founders.

  • Founder effect may also occur, when a few members of a population are blown by a storm to a new island.

The Bottleneck Effect: A sudden change in the environment, such as a fire or flood, may drastically reduce the size of a population. This severe drop in population size can cause bottleneck effect.

  • Population has passed through a “bottleneck” that reduces its size.
  • Bottleneck effect causes sudden reduction in the number of alleles in a population.
  • It causes certain alleles may be over-represented among the survivors, others may be under-represented, and some may be absent altogether.
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