Muller s ratchet

As a search technique, using mutation and selection alone has several limitations. Evolution via asexual reproduction tends to build up deleterious mutations, ultimately limiting the potential of the experiment, an effect known as Muller s ratchet (Muller, 1964). This effect is exacerbated by high mutagenesis rates, as slightly deleterious amino acid substitutions can hitchhike with positive mutations. Recombination can act to remove neutral and deleterious mutations while allowing the accumulation of... 

In a landmark paper, Muller (1964) demonstrated that clonal lineages may be subject to reduce fitness due to a relentless increase in the load of deleterious mutations, and that sexual recombination would tend to reduce that load. The progressive increase in deleterious mutations has become known as Muller s ratchet, and there is evidence for the ratchet in nonrecombining genomes present in eukaryotic cells, namely, mitochondrial DNA (Lynch, 1997 Moran, 1996), sex chromosomes, and Drosophila chromosomes that are prevented from recombining (Rice, 1994). A potential consequence of the ratchet is extinction of clonal lineages (Lynch et al., 1993). Some models indicate that clonal species... 

Currently the evidence does not strongly favor either possibility for hybrid fitness selection on pyramided traits such as alkaloids, or Muller s ratchet. It seems likely that both of these forces may be operative separately in some circumstances, and together in others. 

Bidochka MJ, De Koning J. Are teleomorphs really necessary modeling the potential effects of Muller s ratchet on deuteromycetous entomopathogenic fungi. Mycol Res 105 1014-1019, 2001. 

Butcher D. Muller s ratchet, epistasis and mutation effects. Genetics 141 431 -437, 1995. 

Gordo I, Charlesworth B. The degeneration of asexual haploid populations and the speed of Muller s ratchet. Genetics 154 1379-1387, 2000. 

Nowak MA, Schuster P (1989) Error thresholds of replication in finite populations. Mutation frequencies and the onset of Muller s ratchet. J Theor Biol 137 375-395. doi 10.1016/S0022-5193(89)80036-0... 

Kettner C, Reimann P, Hanggi P, Muller F (2000) Drift ratchet. Phys Rev E 61 312-323 Kleimann P, Linnros J, Petersson S (2000) Formation of wide and deep pores in silicon by electrochemical etching. Mater Sci Eng B 69-70 29-33 Kooij S, Vanmaekelbergh D (1997) Catalysis and pore initiation in the anodic dissolution of silicon in HF. J Electrochem Soc 144 1296-1301... 

Matthias S, Muller F (2003) Asymmetric pores in a silicon membrane acting as massively parallel brownian ratchets. Nature 424 53-57... 

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