Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The genome contains a greater amount of neutral polymorphism in the regions that also have the greatest frequency of genetic recombination (Takahata 1996).This is possibly partly because the processes of genetic recombination are usually accompanied by the formation of some types of mutations (Marais, Mouchiroud, & Duret 2001).However, an elevated mutation rate, accompanying recombination, apparently does not have a decisive effect on the occurrence of the given phenomenon.In contrast to intraspecies polymorphism, divergence in the DNA sequence between closely related species, i.e. interspecies diversity, is not correlated with the frequency of genetic recombination in the given DNA section (Hey 1999; Aquadro, Begun, & Kindahl 1994).It seems that this is probably a consequence of the action of genetic draft, also called hitchhiking, and both its components, background selection and selective sweep (Charlesworth & Guttman 1996; Hey 1999; Otto 2000).In background selection, neutral mutations are removed from the gene pool of the population, because they are located on a chromosome in the vicinity of newly formed selectively negative mutations and are eliminated together with them.In selective sweep, on the other hand, neutral polymorphism disappears because, from time to time, an allele containing a positive mutation is fixed in the population.In both cases, only mutations located sufficiently close to the relevant (negatively or positively) allele are affected.This means that, in sections of the genome with limited crossing-over frequency, both processes are especially effective and can even completely eliminate all polymorphism.This phenomenon can be responsible for low polymorphism in the unrecombined parts of the sex heterochromosome (Kreitman 1996)and, to a considerable degree, also for species cohesion in organisms without sexual reproduction (see XX.2.2.4.3).

            The terminology related to genetic draft is not yet firmly established.A number of authors use the term evolutionary hitchhiking (draft) basically as a synonym for the term selective sweep, while background selection is not included in the category of evolutionary hitchhiking (Aquadro, Begun, & Kindahl 1994).