B {\displaystyle spq} Supposing there is selection against a deleterious allele. μ respectively, where µ = frequency of new mutant alleles per locus per generation µ = 10 -6 : 1 in 1,000,000 gametes has new mutant {\displaystyle \mu } {\displaystyle q={\sqrt {\mu /s}}} [3] Nevertheless, the concept is still widely used in evolutionary genetics, e.g. {\displaystyle 1-hs} q . Mutation–selection balance was originally proposed to explain how genetic variation is maintained in populations, although several other ways for deleterious mutations to persist are now recognized, notably balancing selection. {\displaystyle 1-\mu } Mutation–selection balance is an equilibrium in the number of deleterious alleles in a population that occurs when the rate at which deleterious alleles are created by mutation equals the rate at which deleterious alleles are eliminated by selection. At that equilibrium, µ € µ=sq2. s [3] Thus, provided that the mutant allele is not weakly deleterious (very small balance between selective loss of variation and creation of variation by beneficial mutations).[6]. p / p {\displaystyle q} = s {\displaystyle q} Putting these two pieces together, we can write the expression for the change in allele frequency that is due to BOTH gene flow and selection: Dq = -m(qx t- qy t) - sqx2(1-qx). p and B s B − p B p {\displaystyle h=0} 2 indicates that A is completely dominant while h is small). h of normal alleles A increases at rate / As a simple example of mutation-selection balance, consider a single locus in a haploid population with two possible alleles: a normal allele A with frequency MUTATION-SELECTION BALANCE. 0 μ ; thus In a diploid population, a deleterious allele B may have different effects on individual fitness in heterozygotes AB and homozygotes BB depending on the degree of dominance of the normal allele A. / Mutation-selection balance can maintain a genetic polymorphism. , and so the frequency of deleterious alleles is Herron, JC and S Freeman. A Learn how and when to remove this template message, "De Novo Rearrangements Found in 2% of Index Patients with Spinal Muscular Atrophy: Mutational Mechanisms, Parental Origin, Mutation Rate, and Implications for Genetic Counseling", "Beneficial Mutation–Selection Balance and the Effect of Linkage on Positive Selection", https://en.wikipedia.org/w/index.php?title=Mutation–selection_balance&oldid=976844169, Short description is different from Wikidata, Wikipedia articles that are too technical from September 2010, Creative Commons Attribution-ShareAlike License, This page was last edited on 5 September 2020, at 11:13. {\displaystyle \mu } , and the reverse beneficial mutation from B to A occurs rarely enough to be negligible (e.g. q The degree of dominance affects the relative importance of selection on heterozygotes versus homozygotes. h p B {\displaystyle \mu } − Mutation–selection balance occurs when these forces cancel and 1 . Evolutionary Analysis, 5th Edition. ≈ is not close to zero), then deleterious mutations are primarily removed by selection on heterozygotes because heterozygotes contain the vast majority of deleterious B alleles (assuming that the deleterious mutation rate , and a mutated deleterious allele B with frequency Pearson. q {\displaystyle \mu p} {\displaystyle 1-s} is constant from generation to generation, implying A / 1 q by an amount {\displaystyle p_{AA}} μ A How can we calculate the equilibrium gene frequencies that result from mutation-selection balance. s q [1] This equilibrium frequency is potentially substantially larger than for the case of partial dominance, because a large number of mutant alleles are carried in heterozygotes and are shielded from selection. = 1 p A In this case, we can work out the equilibrium frequency of the mutation: the equilibrium is between the rate at which the mutant gene arises by recurrent mutation, and its elimination by natural selection. Eventually, it will be lost from the population. μ {\displaystyle q} when rate of replacement (by mutation) balances rate of removal (by selection). + be the frequencies of the corresponding genotypes. s {\displaystyle p} B because the mutation rate is so low that {\displaystyle q\approx \mu /hs} 2014. q by an amount 1 = μ , which has a small relative fitness disadvantage of Selection against deleterious dominant Increase in frequency due to mutation Because selection and mutation are opposing forces, they balance each other to create an equilibrium Or, , If we assume that the mutant is rare, then q 2 is very small and all term with q 2 go to zero Also, if mutant is rare, then q m is vanishingly small indicates no dominance). . p For simplicity, suppose that mating is random. and {\displaystyle 1} h measuring the degree of dominance ( , while mutation creates more deleterious alleles increasing {\displaystyle 0} 1 {\displaystyle s} New alleles will be formed by mutation at some rate µ per generation. h and selection acts on heterozygotes with selection coefficient = s The frequency {\displaystyle q} ) and the mutation rate is not very high, the equilibrium frequency of the deleterious allele will be small.