GENETIC DRIFT (Syllabus: GS Paper 3– Sci and Tech)

Context: Genetic drift, not natural selection, was recently identified as the main factor driving speciation in endangered pupfish species.

Genetic Drift

• Definition: It is an evolutionary change in allelic frequencies of a population as a matter of chance.

oGenetic drift describes random fluctuations in the numbers of gene variants in a population.

oIt takes place when the occurrence of variant forms of a gene, called alleles, increases and decreases by chance over time.

oThese variations in the presence of alleles are measured as changes in allele frequencies.

• Population Size: It occurs in very small populations, but its effects are strong.
• Cause: Occurs due to an error in selecting the alleles for the next generation from the gene pool of the current generation.
• Environmental Independence: It does not occur due to any environmental influences.
• Stability in Large Populations: In large populations, the allele frequency of the genes remains relatively stable because the genes are not affecting fitness and do not have a natural selection pressure against the alleles.
• Types of Genetic Drift

oBottleneck Effect: Population size severely decreases due to competition, predators, or diseases.

oFounder Effect: A new population is founded in a new location due to physical or geographical barriers. The new population formed does not interact and mate with the original population.

Gene Flow

• About: Gene flow entails the transfer of genes among populations, species, or organisms, exemplified by bacterial gene transfer. Conversely, genetic drift involves the random selection of genes within a population.
• Migration: Gene flow arises when individuals migrate from one population to another and interbreed.