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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]
Balancer chromosomes were first used in the fruit fly by Hermann Muller, who pioneered the use of radiation for organismal mutagenesis. [2]In the modern usage of balancer chromosomes, random mutations are first induced by exposing living organisms with otherwise normal chromosomes to substances which cause DNA damage; in flies and nematodes, this usually occurs by feeding larvae ethyl ...
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 ...
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 ...
Slightly deleterious mutations are reliably purged only when their selection coefficient are greater than one divided by the effective population size. In larger populations, a higher proportion of mutations exceed this threshold for which genetic drift cannot overpower selection, leading to fewer fixation events and so slower molecular evolution.
For neutral mutations, the rate of fixation per generation is equal to the mutation rate per replication. A relatively constant mutation rate thus produces a constant rate of change per generation (molecular clock). Slightly deleterious mutations with a selection coefficient less than a threshold value of 1 / the effective population size can ...
The worst of these mutations are selected against, leading to the loss of other alleles that are genetically linked to them, in a process of background selection. [2] For recessive harmful mutations, this selection can be enhanced as a consequence of the bottleneck, due to genetic purging. This leads to a further loss of genetic diversity.