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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]
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 Nearly neutral theory stems from the prediction of neutral theory that the balance between selection and genetic drift depends on effective population size. [29] Nearly neutral mutations are those that carry selection coefficients less than the inverse of twice the effective population size. [30]
Selection acts on variation in phenotypes, which are often the result of mutations in protein-coding genes. The genetic code is written in DNA sequences as codons , groups of three nucleotides . Each codon represents a single amino acid in a protein chain.
This is a diagram of a multiple origin soft selective sweep from recurrent mutation. It shows the different steps (a beneficial mutation occurs and increases in frequency, but before it fixes the same mutation occur again on a second genomic background, together, the mutations fix in the population) and the effect on nearby genetic variation.
A hitchhiker mutation (or passenger mutation in cancer biology) may itself be neutral, advantageous, or deleterious. [ 7 ] Recombination can interrupt the process of genetic hitchhiking, ending it before the hitchhiking neutral or deleterious allele becomes fixed or goes extinct. [ 6 ]
In 1950, James F. Crow offered two different explanations (later dubbed the classical and balance positions) based on the paradox first articulated by J. B. S. Haldane in 1937: the effect of deleterious mutations on the average fitness of a population depends only on the rate of mutations (not the degree of harm caused by each mutation) because ...