• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of geneticsGeneticsCurrent IssueInformation for AuthorsEditorial BoardSubscribeSubmit a Manuscript
Genetics. Mar 2000; 154(3): 1379–1387.
PMCID: PMC1460994

The degeneration of asexual haploid populations and the speed of Muller's ratchet.


The accumulation of deleterious mutations due to the process known as Muller's ratchet can lead to the degeneration of nonrecombining populations. We present an analytical approximation for the rate at which this process is expected to occur in a haploid population. The approximation is based on a diffusion equation and is valid when N exp(-u/s) >> 1, where N is the population size, u is the rate at which deleterious mutations occur, and s is the effect of each mutation on fitness. Simulation results are presented to show that the approximation estimates the rate of the process better than previous approximations for values of mutation rates and selection coefficients that are compatible with the biological data. Under certain conditions, the ratchet can turn at a biologically significant rate when the deterministic equilibrium number of individuals free of mutations is substantially >100. The relevance of this process for the degeneration of Y or neo-Y chromosomes is discussed.

Full Text

The Full Text of this article is available as a PDF (180K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Drake JW, Charlesworth B, Charlesworth D, Crow JF. Rates of spontaneous mutation. Genetics. 1998 Apr;148(4):1667–1686. [PMC free article] [PubMed]
  • Felsenstein J. The evolutionary advantage of recombination. Genetics. 1974 Oct;78(2):737–756. [PMC free article] [PubMed]
  • Fry JD, Keightley PD, Heinsohn SL, Nuzhdin SV. New estimates of the rates and effects of mildly deleterious mutation in Drosophila melanogaster. Proc Natl Acad Sci U S A. 1999 Jan 19;96(2):574–579. [PMC free article] [PubMed]
  • Gessler DD. The constraints of finite size in asexual populations and the rate of the ratchet. Genet Res. 1995 Dec;66(3):241–253. [PubMed]
  • Gessler DD, Xu S. On the evolution of recombination and meiosis. Genet Res. 1999 Apr;73(2):119–131. [PubMed]
  • Haigh J. The accumulation of deleterious genes in a population--Muller's Ratchet. Theor Popul Biol. 1978 Oct;14(2):251–267. [PubMed]
  • Keightley PD. Nature of deleterious mutation load in Drosophila. Genetics. 1996 Dec;144(4):1993–1999. [PMC free article] [PubMed]
  • Kimura M, Maruyama T. The mutational load with epistatic gene interactions in fitness. Genetics. 1966 Dec;54(6):1337–1351. [PMC free article] [PubMed]
  • Kondrashov AS. Muller's ratchet under epistatic selection. Genetics. 1994 Apr;136(4):1469–1473. [PMC free article] [PubMed]
  • Lahn BT, Page DC. Four evolutionary strata on the human X chromosome. Science. 1999 Oct 29;286(5441):964–967. [PubMed]
  • Lynch M, Bürger R, Butcher D, Gabriel W. The mutational meltdown in asexual populations. J Hered. 1993 Sep-Oct;84(5):339–344. [PubMed]
  • Butcher D. Muller's ratchet, epistasis and mutation effects. Genetics. 1995 Sep;141(1):431–437. [PMC free article] [PubMed]
  • Orr HA, Kim Y. An adaptive hypothesis for the evolution of the Y chromosome. Genetics. 1998 Dec;150(4):1693–1698. [PMC free article] [PubMed]
  • Pamilo P, Nei M, Li WH. Accumulation of mutations in sexual and asexual populations. Genet Res. 1987 Apr;49(2):135–146. [PubMed]
  • Charlesworth B. The evolution of chromosomal sex determination and dosage compensation. Curr Biol. 1996 Feb 1;6(2):149–162. [PubMed]
  • Prügel-Bennett A. Modelling evolving populations. J Theor Biol. 1997 Mar 7;185(1):81–95. [PubMed]
  • Charlesworth B, Charlesworth D. Rapid fixation of deleterious alleles can be caused by Muller's ratchet. Genet Res. 1997 Aug;70(1):63–73. [PubMed]
  • Rice WR. Degeneration of a nonrecombining chromosome. Science. 1994 Jan 14;263(5144):230–232. [PubMed]
  • Steinemann M, Steinemann S. Enigma of Y chromosome degeneration: neo-Y and neo-X chromosomes of Drosophila miranda a model for sex chromosome evolution. Genetica. 1998;102-103(1-6):409–420. [PubMed]
  • Steinemann M, Steinemann S, Lottspeich F. How Y chromosomes become genetically inert. Proc Natl Acad Sci U S A. 1993 Jun 15;90(12):5737–5741. [PMC free article] [PubMed]
  • Steinemann S, Steinemann M. The Amylase gene cluster on the evolving sex chromosomes of Drosophila miranda. Genetics. 1999 Jan;151(1):151–161. [PMC free article] [PubMed]
  • Stephan W, Chao L, Smale JG. 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. [PubMed]

Articles from Genetics are provided here courtesy of Genetics Society of America


Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


  • MedGen
    Related information in MedGen
  • PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...