Genetic hitchhiking

Genetic hitchhiking, also called genetic draft or the hitchhiking effect, is a change in the frequency of an allele that occurs not because natural selection is acting on that allele directly, but because it sits close, on the same stretch of DNA, to another gene undergoing a selective sweep. When a gene experiences such a sweep, a rapid rise in frequency driven by an advantageous mutation, nearby genetic variants linked to it in linkage disequilibrium shift in frequency along with it; neutral, or even mildly harmful, alleles that happen to lie close by on the chromosome are carried along, or hitchhike, with the sweep. How strongly an allele hitchhikes depends on its physical proximity to the selected gene and on recombination, which can break the two apart before the hitchhiking allele becomes fixed in the population or is lost; the closer the two sit together, the less chance recombination has to separate them. Genetic hitchhiking, together with its mirror process, background selection, in which deleterious mutations pull down the frequency of nearby neutral variants, is treated as a stochastic evolutionary force similar in effect to genetic drift, even though it works through genetic linkage rather than random sampling. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/