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The impact of deleterious mutations on the transition to meiotic sex and the structure of the germline

Colnaghi, Marco; (2022) The impact of deleterious mutations on the transition to meiotic sex and the structure of the germline. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The accumulation of deleterious mutations predicted by Muller’s ratchet – the progressive increase in mutation load caused by genetic drift – can cause the extinction of asexual populations and is considered one of the forces behind the maintenance of sex, the evolution of sex chromosomes, and the loss of genetic information in inversions. Here, I investigate the extent to which this process has influenced, constrained, and shaped the evolution of life. Using theoretical and computational models, I demonstrate that the need for increased purifying selection played a key role in major evolutionary transitions, focussing on the origin of meiotic sex and the evolution of the female germline. Early models of the origin of sex have generally focussed on the transition from asexual to sexual lifestyle. It is now universally accepted that prokaryotes undergo homologous recombination via lateral gene transfer (LGT), which can prevent the mutational meltdown predicted by Muller’s ratchet. Here, I investigate the origin of sex as part of the transition from prokaryotes to eukaryotes. I develop a theoretical model to investigate the impact of the increase in genome size and density of genomic repeats that took place during eukaryogenesis. My results indicate that these conditions led to the failure of LGT, generating a strong selective pressure for the origin of meiotic sex. But while meiotic sex can facilitate purifying selection on nuclear genes, it cannot prevent the accumulation of mutations in mitochondrial DNA (mtDNA). I demonstrate that the need to preserve mtDNA against Muller’s ratchet caused the evolution of tight mechanisms for mitochondrial quality control, shaping the evolution of the female germline in metazoans. This theoretical framework can be applied to a wide range of biological processes, including bacterial evolution, genome streamlining in organelles and endosymbionts, and the evolution of a two-step meiosis.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The impact of deleterious mutations on the transition to meiotic sex and the structure of the germline
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Computer Science
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Genetics, Evolution and Environment
UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10143516
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