Mutation-selection+balance

=Mutation-selection balance=

A genetic variant caused by mutation that is deleterious may not immediately be removed from the population. The frequency of the variant upon appearing in the population is 1/N (or 1/2N in a diploid population) and this value may drift up or down before returning to zero. In an infinitely sized population, the frequency would never return to zero; the forces of mutation and selection counteract each other until the frequency reaches some equilibrium. This is called the **mutation-selection balance**.

The equilibrium frequency, //f//, of a mutant allele for a haploid population or the dominant allele of a diploid population is //f// = µ///s// where µ is the rate of mutation and //s// is the deleterious selection coefficient (the decrease in relative fitness). For recessive alleles in a diploid population, //f// = √ µ///s//. A useful approximation for alleles of intermediate dominance is //f// ~ μ / (//sh//) where //h// is the coefficient of dominance. All of these formulae are approximations because they ignore back-mutations, typically a trivial effect.