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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]
The incidental purging of non-deleterious alleles due to such spatial proximity to deleterious alleles is called background selection. [4] This effect increases with lower mutation rate but decreases with higher recombination rate. [5] Purifying selection can be split into purging by non-random mating (assortative mating) and purging by genetic ...
In negative frequency-dependent selection, the fitness of a phenotype or genotype decreases as it becomes more common. This is an example of balancing selection. More generally, frequency-dependent selection includes when biological interactions make an individual's fitness depend on the frequencies of other phenotypes or genotypes in the ...
Purifying or negative selection acts to remove genetic variation from the population (and is opposed by de novo mutation, which introduces new variation. [76] [77] In contrast, balancing selection acts to maintain genetic variation in a population, even in the absence of de novo mutation, by negative frequency-dependent selection.
For example, if K a /K s = 1, it could be due to relaxed selection, or to a chimera of positive and purifying selection at the locus. A solution to this limitation would be to apply K a /K s analysis across many species at individual codons. The K a /K s method requires a rather strong signal in
Genetic purging is the increased pressure of natural selection against deleterious alleles prompted by inbreeding. [1]Purging occurs because deleterious alleles tend to be recessive, which means that they only express all their harmful effects when they are present in the two copies of the individual (i.e., in homozygosis).
Tajima's D is a population genetic test statistic created by and named after the Japanese researcher Fumio Tajima. [1] Tajima's D is computed as the difference between two measures of genetic diversity: the mean number of pairwise differences and the number of segregating sites, each scaled so that they are expected to be the same in a neutrally evolving population of constant size.
For example, mutational biases and purifying selection favoring conservative changes are probably both responsible for the relatively high rate of transitions compared to transversions in evolving sequences. However, the Kimura (K80) model described below only attempts to capture the effect of both forces in a parameter that reflects the ...