Hitch-hiking describes the situation where alleles are given a lift in frequency because selection is favoring alleles at other loci with which they are associated.
Suppose that directional selection is substituting one allele A ' for another A at one locus, and there is a neutral polymorphism (B1B2) at a linked locus.
Whichever of B1 and B2 happened to be linked with A ' when it arose as a mutant will have its frequency increased. If the new mutant A ' happened to arise on a B1-bearing chromosome, then B1 will eventually be fixed together with the selected allele A '.
An animation illustrates the hitch-hiking process.
How is hitch-hiking related to the neutral theory?