SELECTIVE SWEEP AND THE SIZE OF THE HITCHHIKING SET

Just after the fixation of an advantageous allele in the population (this spread is called a selective sweep), the neutral genes close to the site under selection tend to have the same ancestor as the gene under selection. However, some recombinations may occur during the selective sweep and break the link, which reduces the number of hitchhiking alleles. We consider a large selection coefficient alpha and extend the results of Etheridge; Pfaffelhuber and Wakolbinger (2006) and the work of Pfaffelhuber and Studeny (2007) about genetic hitchhiking, where the recombination rate scales with alpha/ log alpha. We first describe the genealogy at an arbitrary number of partially linked neutral loci, with an order of accuracy of (1/(log alpha)(2)) in total variation. Then, we use this framework to obtain an approximate distribution for the size of the hitchhiking set at the end of the selective sweep, with the same accuracy.