Abstract
In a finite asexual population mean fitness may decrease by a process known as Muller's ratchet, which proceeds if all individuals with the minimum number of deleterious alleles are randomly lost. If these alleles have independent effects on fitness, previous analysis suggested that the rate of this decrease either remains constant or, if accumulation of mutations leads to the decline of the population size, grows. Here I show that this conclusion is quite sensitive to the assumption of independence. If deleterious alleles have synergistic fitness effects, then, as the ratchet advances, the frequency of the best available genotype will necessarily increase, making its loss less and less probable. As a result, sufficiently strong synergistic epistasis can effectively halt the action of Muller's ratchet. Instead of being driven extinct, a finite asexual population could then survive practically indefinitely, although with lower mean fitness than without random drift.
Full Text
The Full Text of this article is available as a PDF (440.1 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Houle D., Hoffmaster D. K., Assimacopoulos S., Charlesworth B. The genomic mutation rate for fitness in Drosophila. Nature. 1992 Sep 3;359(6390):58–60. doi: 10.1038/359058a0. [DOI] [PubMed] [Google Scholar]
- KIMURA M., MARUYAMA T., CROW J. F. THE MUTATION LOAD IN SMALL POPULATIONS. Genetics. 1963 Oct;48:1303–1312. doi: 10.1093/genetics/48.10.1303. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kimura M., Maruyama T. The mutational load with epistatic gene interactions in fitness. Genetics. 1966 Dec;54(6):1337–1351. doi: 10.1093/genetics/54.6.1337. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kondrashov A. S. Classification of hypotheses on the advantage of amphimixis. J Hered. 1993 Sep-Oct;84(5):372–387. doi: 10.1093/oxfordjournals.jhered.a111358. [DOI] [PubMed] [Google Scholar]
- Lynch M., Bürger R., Butcher D., Gabriel W. The mutational meltdown in asexual populations. J Hered. 1993 Sep-Oct;84(5):339–344. doi: 10.1093/oxfordjournals.jhered.a111354. [DOI] [PubMed] [Google Scholar]
- MULLER H. J. THE RELATION OF RECOMBINATION TO MUTATIONAL ADVANCE. Mutat Res. 1964 May;106:2–9. doi: 10.1016/0027-5107(64)90047-8. [DOI] [PubMed] [Google Scholar]
- Mukai T., Chigusa S. I., Mettler L. E., Crow J. F. Mutation rate and dominance of genes affecting viability in Drosophila melanogaster. Genetics. 1972 Oct;72(2):335–355. doi: 10.1093/genetics/72.2.335. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Shnol E. E., Kondrashov A. S. The effect of selection on the phenotypic variance. Genetics. 1993 Jul;134(3):995–996. doi: 10.1093/genetics/134.3.995. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Stephan W., Chao L., Smale J. G. The advance of Muller's ratchet in a haploid asexual population: approximate solutions based on diffusion theory. Genet Res. 1993 Jun;61(3):225–231. doi: 10.1017/s0016672300031384. [DOI] [PubMed] [Google Scholar]