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Neutral mutation

Nucleotide site Selectively advantageous mutation

Figure 8.22 The impact of natural selection on an advantageous mutation as well as on associated nucleotide sites, often called a selective sweep. Imagine a single population that contains five distinct DNA sequences without recombination because reproduction is clonal. Each DNA sequence is distinguished by a number of neutral mutations (blue circles) and has a frequency given by the histogram on the left. Initially, the population has polymorphism since the population is composed of intermediate frequencies of each DNA sequence. At time 0, the third DNA sequence experiences a mutation that is strongly advantageous, indicated by the star. Natural selection acts to increase the frequency of the advantageous mutation over time, until the population approaches fixation for the third DNA sequence. Once selection has swept the advantageous mutation to near fixation the population has very little polymorphism. This is because only those original neutral mutations that were linked to the advantageous allele on the same DNA sequence remain in the population. Thus, positive selection on one site also sweeps away polymorphism at linked nucleotide sites if gametic disequilibrium is maintained. The figure assumes that positive natural selection is strong and increases the frequency of the third DNA sequence rapidly such that no new mutations appear in the population.

in complete gametic disequilibrium with two neighboring neutral mutations that happened to be on that chromosome.

Maynard Smith and Haigh (1974) coined the term genetic hitch-hiking to describe the consequences

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