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CONSIDERATION OF MULLER'S RATCHET MECHANISM THROUGH STUDIES OF GENETIC LINKAGE AND GENOMIC COMPATIBILITIES IN CLONALLY REPRODUCING POECILIOPSIS
Author(s) -
Leslie James F.,
Vrijenhoek Robert C.
Publication year - 1980
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1980.tb04051.x
Subject(s) - biology , mechanism (biology) , linkage (software) , ratchet , evolutionary biology , genetics , gene , epistemology , work (physics) , mechanical engineering , philosophy , engineering
The generation of all-female offspring can provide a twofold reproductive advantage for an asexual lineage (MaynardSmith, 1978). This reproductive benefit should be most pronounced in the low fecundity, higher organisms, such as birds and mammals; therefore, the absence of asexuality in these groups poses a paradox for evolutionary biologists (Williams, 1975). Most theoretical considerations of the costs of asexuality are extensions or debates of the argument that clones lack evolutionary flexibility because they must rely only on the rate of beneficial mutations for adaptive evolution. Since harmful mutations occur far more frequently than beneficial ones, a species without genetic recombination might also be subject to genetic deterioration (FeIsenstein, 1974). Both sexual and asexual lineages, initially free of detrimental genes, will accumulate mutations at the same rate, until a mutation/selection equilibrium is reached. At this point, an asexual lineage has a "rachet mechanism" (Muller, 1964) such that its load of mutations cannot decrease below that already present in its least loaded clones, but the load can increase. The effectiveness of the ratchet mechanism in causing genetic deterioration depends upon the size of the genome (more loci to mutate) and the size of the population (Maynard-Smith, 1978). In small populations, random processes can result in the