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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.
A multiple origin soft sweep happens when mutations are common, for example in a large population, so that the same or similar beneficial mutations occur on a different genomic background such that no single genomic background can hitchhike the high frequency. [2] Whether the selective sweep has occurred can be explored in various ways.
Tajima's D is a population genetic test statistic created by and named after the Japanese researcher Fumio Tajima. [1] Tajima's D is computed as the difference between two measures of genetic diversity: the mean number of pairwise differences and the number of segregating sites, each scaled so that they are expected to be the same in a neutrally evolving population of constant size.
Selective sweeps happen when newly appeared (and hence still rare) mutations are advantageous and increase in frequency. Neutral or even slightly deleterious alleles that happen to be close by on the chromosome 'hitchhike' along with the sweep.
The sequence just experienced a bout of selective sweep (an allele rose to fixation/near fixation), so all alleles became homogenized. The rare polymorphisms you see are very recent, or; There was a population bottleneck, so all individuals in the population are derived from a small set (or one) common ancestor
Soft selective sweep; Stabilizing selection; Supercow (dairy) This page was last edited on 29 August 2020, at 17:49 (UTC). Text is available under the Creative ...
When adaptation stems from the species pool of standing genetic variation, a "soft sweep", the rationale does not apply, because the allele is no longer rare in the beginning of the sweep. In fact, recessive alleles are more likely to sweep than dominant sweeps when alleles are previously maintained in the population.
Since a selective sweep also results in selection of neighbouring alleles, the presence of a block of strong linkage disequilibrium might indicate a 'recent' selective sweep near the centre of the block. [111] Background selection is the opposite of a selective sweep. If a specific site experiences strong and persistent purifying selection ...