The role of recombination and hybridisation in adaptive evolution

Ward, Benjamin (2017) The role of recombination and hybridisation in adaptive evolution. Doctoral thesis, University of East Anglia.

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As one of the five evolutionary forces, recombination fulfills both a cleansing
role, as well as a role in generating genetic diversity. Recombination
cleanses by separating deleterious mutations from their genomic background,
increasing the efficacy of purifying selection and curtailing the
continuous accumulation of deleterious mutations. Recombination also
plays a fundamental role in the repair of damaged DNA, and it can be a
creative force, resulting in the formation of novel genotypes, haplotypes
and alleles, thereby playing a key role in adaptive evolution. By uniting
beneficial mutations that exist at different loci in separate lineages, meiotic
recombination during sex accelerates adaptive evolution. Although
recombination leaves a distinct signature or footprint in the genome of
organisms, identifying this force can be difficult; subsequent recombination
events tend to wipe out their past genomic footprints. This thesis presents
the development of a novel software package called HybridCheck, for the
detection of genomic regions affected by recombination in Next Generation
Sequence data, and the rapid molecular dating of recombination events.
Hybrid-Check was used to analyze recombination signal in different races
of the plant pathogen Albugo candida, a generalist obligate biotroph that
infects Brassica plants. I show that recombination facilitated occasional
introgression and gene flow between host-specialized races. This may
have accelerated the rate of adaptive evolution, and possibly broadened
the pathogen’s host-range. Finally, the genome of the polar diatom Fragilar-
iopsis cylindrus contains diverged alleles that are differentially expressed in
different environmental conditions. The hypothesis that ancient asexuality
explains how the diverged alleles evolved is challenged, but not rejected,
based on evidence of recombination presented in this thesis. An alternative
hypothesis is proposed: allelic divergence might have evolved despite
the homogenizing effect of meiotic recombination as a result of very large
effective population sizes and strong diversifying selection on F. cylindrus
in the polar environment.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Users 4971 not found.
Date Deposited: 06 Apr 2017 10:06
Last Modified: 06 Apr 2017 10:06


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