Hermisson and Pennings (2005) introduced the term “soft sweep” to describe a situation in which multiple beneficial alleles (with a common origin or from recurrent mutations) increase in in frequency in a population at one time. They contrasted this with a traditional or “hard” selective sweep that results in loss of variation around the beneficial allele as linked variants (at nearby loci) hitchhike on the beneficial allele’s success. Because different beneficial alleles at the same locus will be present on different backgrounds, soft sweeps reduce the degree to which selective sweeps decrease variation. Soft sweeps are more likely when recurrent mutations are common and/or when the contribution of standing genetic variation to adaptation is significant (with these parameters carefully explored by Hermisson and Pennings, 2005). This review paper also offers a nice summary.
This is not my idea, but this is my blog. My aim is to alert readers to good ideas that are out there in the recent literature. Evolution is a conceptually rich field, and I hope to showcase some of this richness, but I will emphasise studies in experimental evolution. My prejudice is that these put evolutionary ideas on a firmer footing and also into a suitable context.
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