Mutation–selection balance
This article may be too technical for most readers to understand.(September 2010) |
Mutation–selection balance is an equilibrium in the number of deleterious alleles in a population that occurs when the rate at which deleterious alleles are created by mutation equals the rate at which deleterious alleles are eliminated by selection.[1][2][3][4] The majority of genetic mutations are neutral or deleterious; beneficial mutations are relatively rare. The resulting influx of deleterious mutations into a population over time is counteracted by negative selection, which acts to purge deleterious mutations. Setting aside other factors (e.g., balancing selection, and genetic drift), the equilibrium number of deleterious alleles is then determined by a balance between the deleterious mutation rate and the rate at which selection purges those mutations.
Mutation–selection balance was originally proposed to explain how
Haploid population
As a simple example of mutation-selection balance, consider a single
Diploid population
In a
The degree of dominance affects the relative importance of selection on heterozygotes versus homozygotes. If A is not completely dominant (i.e. is not close to zero), then deleterious mutations are primarily removed by selection on heterozygotes because heterozygotes contain the vast majority of deleterious B alleles (assuming that the deleterious mutation rate is not very large). This case is approximately equivalent to the preceding haploid case, where mutation converts normal homozygotes to heterozygotes at rate and selection acts on heterozygotes with selection coefficient ; thus .[1]
In the case of complete dominance (), deleterious alleles are only removed by selection on BB homozygotes. Let , and be the frequencies of the corresponding genotypes. The frequency of normal alleles A increases at rate due to the selective elimination of recessive homozygotes, while mutation causes to decrease at rate (ignoring
Many properties of a non random mating population can be explained by a random mating population whose effective population size is adjusted. However, in non-steady state population dynamics there can be a lower prevalence for recessive disorders in a random mating population during and after a growth phase.[7][8]
See also
References
- ^ ISBN 9781932846126.
- PMID 20594608.
- ^ ISBN 9780879696849.
- ^ a b Herron, JC and S Freeman. 2014. Evolutionary Analysis, 5th Edition. Pearson.
- PMID 9345102.
- PMID 17483432.
- arXiv:2012.04968 [q-bio.PE].
- ^ "visualization of effects of different mating schemes". YouTube.