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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 genetic variation is ...
Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. Balancing selection is rare compared to purifying selection. [1]
Nearly neutral mutations are those that carry selection coefficients less than the inverse of twice the effective population size. [30] The population dynamics of nearly neutral mutations are only slightly different from those of neutral mutations unless the absolute magnitude of the selection coefficient is greater than 1/N, where N is the ...
At the same time, new mutations occur, resulting in a mutation–selection balance. The exact outcome of the two processes depends both on the rate at which new mutations occur and on the strength of the natural selection, which is a function of how unfavourable the mutation proves to be.
The Haldane-Muller theorem of mutation–selection balance says that the load depends only on the deleterious mutation rate and not on the selection coefficient. [6] Specifically, relative to an ideal genotype of fitness 1, the mean population fitness is exp ( − U ) {\displaystyle \exp(-U)} where U is the total deleterious mutation rate ...
Shifting balance theory aims to explain how this may be possible. The shifting balance theory is a theory of evolution proposed in 1932 by Sewall Wright, suggesting that adaptive evolution may proceed most quickly when a population divides into subpopulations with restricted gene flow.
Individuals with a high mutation rate now increasingly decrease population fitness, and selection causes the mutation rate to decrease again. At the same time, new advantageous alleles have a diminishing positive effect on fitness. At a certain point, natural selection, mutation rate and random genetic drift reach a balance. [7]
Hitchhiking is necessary for the evolution of higher mutation rates to be favored by natural selection on evolvability. A hypothetical mutator M increases the general mutation rate in the area around it. Due to the increased mutation rate, the nearby A allele may be mutated into a new, advantageous allele, A* --M-----A-- -> --M-----A*--