The evolutionary significance of genetic recombination is one of the most intriguing problems in evolutionary biology, since recombination is one of the primary features of sexual reproduction. Of the vast number of questions that one can ask in relation to sex and recombination, the simplest is: what happens in their absence. It was realised long ago that the level of recombination influences the action of natural selection. Non-recombining genomes are expected to adapt more slowly than recombining ones. In addition, they are also more prone to degeneration by the accumulation of harmful mutations. This study is concerned with the latter process: the fate of a non-recombining genome or chromosome that is continuously subject to recurrent mutation to deleterious alleles. H.J. Muller argued that one major difference between a non-recombining asexual and a recombining sexual population is that, in the former, genetic drift can overwhelm selection against deleterious mutations, whereas this not so likely in the presence of recombination. In the absence of recombination, deleterious mutations can therefore accumulate by what Muller called a ratchet-like process. This study focuses on four aspects of this mechanism. First, the quantification of its rate is examined, both by simulation methods and by analytical approximations, under the simplest possible model. Second, its interaction with another phenomenon, the continuous elimination of strongly deleterious alleles, is studied. Third, its effects on neutral DNA polymorphism, and the possibility of detecting its action by measuring these effects, are studied. Fourth, the circumstances under which this process may have significance for the evolution of non-recombining Y chromosomes are analysed. It is hoped that this work represents a useful contribution to a better understanding of Muller’s ratchet. The overall conclusion is that, given the present empirical knowledge on rates and effects of deleterious mutations and on levels and patterns of variability on Y chromosomes, Muller’s ratchet may well be significant in driving their evolution, even in species with large populations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657693 |
| Date | January 2001 |
| Creators | Gordo, Isabel Mendes |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12045 |
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