The recombination landscape of fission yeast: natural variation and the effects of direct selection and inversions on the evolution of recombination

Berenguer Millanes, Cristina (2025): The recombination landscape of fission yeast: natural variation and the effects of direct selection and inversions on the evolution of recombination. Dissertation, LMU München: Faculty of Biology

Abstract

Sex, and therefore meiotic recombination, are almost ubiquitous in the eukaryotic world. Recombination involves the shuffling of genes during meiosis, generating new combination of alleles in the offspring. This process is widely believed to be beneficial for adaptation, as it creates new variation for evolution to act on, and it separates deleterious mutations from beneficial alleles. Recombination comes, however, with costs, such as breaking up combinations that are already beneficial in a certain environment, or possible mechanistic mistakes. Recombination variation in nature – from higher taxonomic clades, to changes in recombination rates within the same chromosome –is influenced by a complex interplay of genetic and environmental factors. Concretely, the discovered genetic factors that control recombination rate variation show that recombination rates not only affect evolution, but are affected by evolution too. Despite decades of research, the mechanisms which regulate recombination rates are still unknown. Using the fission yeast Schizosaccharomyces pombe as a model organism, I elucidate some of the previously unanswered questions about the current variation of recombination rates, and what mechanisms affect them. In the first part of the results, it is shown that recombination rates significantly vary among strains, and within the strains when comparing the three chromosomes. The data indicates that recombination rates in fission yeast could be locally regulated, within distances of few kilobases. To elucidate how this current variation came to be, in my second part of the results I performed an evolutionary experiment where the effect of direct selection in recombination rate changes is proved. Here, recombination rates in two intervals were changed, both increased and decreased, after 36 generations. Finally, the effect of the presence of inversions in heterozygosis, as well as the effect of their size, is tested. These show an effect on recombination both inside and on the flanks of the inverted segment, as well as demonstrating that inversions affect cell viability. These effects depend on size. This work provides a framework for understanding the role that direct selection and genomic rearrangements have on the evolution of recombination rates, and they shed light on how the current variation we observe has been achieved.

• Item Type: Theses (Dissertation, LMU Munich)
• Keywords: meiotic recombination, evolution, fission yeast, pombe
• Subjects: 500 Natural sciences and mathematics; 500 Natural sciences and mathematics > 570 Life sciences
• Faculties: Faculty of Biology
• Language: English
• Date of oral examination: 9. May 2025
• 1. Referee: Nieuwenhuis, Bart
• Signature of the printed copy: 0001/UMC 31259