Recurrent mutation and purifying selection
Recurrent mutation can replenish a deleterious allele that purifying selection removes.
Key knowledge
Recurrent mutation can replenish a deleterious allele that purifying selection removes. In the low-mutation, large random-mating diploid model, a fully recessive deleterious allele can reach an approximate frequency proportional to the square root of mutation rate divided by its homozygous fitness cost. Partial dominance changes the balance because heterozygotes also experience selection.
Values and equations
qeq ≈ √(u/s)
- qeq
- frequency of recessive deleterious allele a 1
- u
- per-generation probability A→a 1 per generation
- s
- relative fitness reduction of aa 1
Conditions and scope
- The displayed recessive approximation assumes one-way mutation, fitnesses AA=Aa=1 and aa=1−s, u much smaller than s, and negligible drift/migration.
- Environmental variation, inbreeding, linkage and dominance can change the equilibrium; an observed rare variant is not proof of this model.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Lecture 8: Selection-Scenario Table, Recessive Mutation–Selection EquilibriumNicholas J. Gotelli — Department of Biology, University of Vermont, BCOR 102 notes (2017)Textbook chapter
- Lecture 19: Mutation–Selection Balance, slide 8Graham Coop — UC Davis, undergraduate Population and Quantitative Genetics EVE 102 (2016)Textbook chapter · PDF
Evidence and review
Read explicit square-root equilibrium in the Vermont selection table and UC Davis low-mutation/dominance context; excluded fixed gene-specific disease rates and unrestricted mean-fitness-maximization claim.
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