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In population genetics, fixation is the change in a gene pool from a situation where there exists at least two variants of a particular gene in a given population to a situation where only one of the alleles remains. That is, the allele becomes fixed. [1]
These random fluctuations within the allele frequencies can lead to the fixation or loss of certain alleles within a population. To the right is an image that shows through successive generations; the allele frequencies fluctuate randomly within a population. The smaller the population size, the faster fixation or loss of alleles will occur.
In population genetics, F-statistics (also known as fixation indices) describe the statistically expected level of heterozygosity in a population; more specifically the expected degree of (usually) a reduction in heterozygosity when compared to Hardy–Weinberg expectation.
In genetics, a selective sweep is the process through which a new beneficial mutation that increases its frequency and becomes fixed (i.e., reaches a frequency of 1) in the population leads to the reduction or elimination of genetic variation among nucleotide sequences that are near the mutation.
When an allele (variant of a gene) drifts to fixation, the other allele at the same locus is lost, resulting in a loss in genetic diversity. [17] In small population sizes, inbreeding , or mating between individuals with similar genetic makeup, is more likely to occur, thus perpetuating more common alleles to the point of fixation, thus ...
Coalescent theory is a model of how alleles sampled from a population may have originated from a common ancestor.In the simplest case, coalescent theory assumes no recombination, no natural selection, and no gene flow or population structure, meaning that each variant is equally likely to have been passed from one generation to the next.
Once an allele becomes fixed, genetic drift comes to a halt, and the allele frequency cannot change unless a new allele is introduced in the population via mutation or gene flow. Thus even while genetic drift is a random, directionless process, it acts to eliminate genetic variation over time.
The main difference between soft and hard selective sweeps lies in the expected number of different haplotypes carrying the beneficial mutation or mutations, and therefore in the expected number of haplotypes that hitchhike to considerable frequency during the selective sweep, and which remain in the population at the time of fixation.