Genetic drift:  Introduction, Types, Roles


  • It is an evolutionary mechanism that describes the change in frequency of an existing gene variant as a result of random fluctuations in the frequency of a specific version of the gene (allele) in a population. In fact, it is an evolutionary shift in allelic frequencies that represents the random fluctuations in the number of gene variations in a population.
  • It also known as the ‘Sewall Wright effect’ which is responsible to change genetic pool in a specific location and time.
  • is a nondirectional process that causing loss of genetic variation from populations, increased homozygosity of the individuals, and genetic differentiation among populations.


The Bottleneck Effect

 (Reduction in the population size)

Natural occurrences such as deteriorating environmental conditions like natural disaster, flood, earthquake, fires, volcanic eruptions can potentially increase genetic drift. The bottleneck effect occurs when just a few individuals survive, reducing variance in the population’s gene pool. The genetic structure of survivors becomes the genetic structure of the entire population.

Afterwards, when the environmental conditions improve again that may differ significantly from the pre-disaster population.

Antibiotics eliminate dangerous microorganisms in your system, regardless of their alleles. Antibiotics significantly reduce dangerous germs. This effectively eliminates illness symptoms. If a patient discontinues their antibiotic treatment early, only a small number will survive. This much smaller population may have allele frequencies that differ significantly from the original bacterial population. These alterations do not reflect the success or failure of the many alleles, but rather the consequences of a random selection of bacteria. The new alleles will dominate the population until selection or more genetic drift causes allele frequencies to shift.

The Founder Effect

(Subset of population founds new population)

 It occurs when a portion of the population (i.e., “founders”) separates from the old population to establish a new population in a new location due to physical or geographical barriers with different allele frequencies.

In this case, it is highly unlikely that those people are representative of the entire population, resulting in the founder effect. The founder effect happens when a population’s genetic structure changes to resemble that of its founding fathers and mothers.

There are many species that are found only on a particular island. This is due to the founder effect.

Roles of genetic drift in evolution:

  • Affects the genetic makeup of the population
  • The evolutionary mechanism fails to develop adaptations.
  • Allele fixing
  • It plays a significant role in the evolution of new species
  • Decreases gene diversity
  • New population genetically distinct from its original population

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