Åpne denne publikasjonen i ny fane eller vindu >>2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]
Identifying the processes involved in the evolution of suppressed recombination between sex chromosomes and understanding their consequences for the evolutionary dynamics of sex-linked loci have been major topics of research during the last century. In this thesis, I used the avian ZW system, where females are the heterogametic sex, to investigate the underlying processes in sex chromosome evolution in birds. I identified the gametologous genes between the largely recombining Z and W chromosomes of ostrich and dated the timing of the cessation of recombination to prior to the split of modern birds. I then constructed a genetic map of the ostrich Z chromosome and corrected its assembly in order to obtain the ancestral organization of the Z chromosome in a basal clade of birds. By analyzing the inversion events across the avian phylogeny, I concluded that a combination of Z- and possibly W-linked inversions might have been responsible for the evolution of suppressed recombination in avian sex chromosomes. To understand the determinants of levels of genetic diversity on Z chromosome compared to autosomes, I calculated Z to autosome (Z:A) genetic diversity across 32 avian species. This revealed a broad range of Z:A genetic diversity, between 0.278 – 1.27. Lineage-specific estimates of the nonsynonymous to synonymous substitution rate ratio (dN:dS) for autosomal and Z-linked genes further revealed a Fast-Z effect in the majority of birds. The lack of a significant correlation between Z:A dN:dS and Z:A genetic diversity indicated that genetic drift might not be sufficient to explain faster evolution of Z-linked genes, suggesting that positive selection might also contribute to the observed values. Finally, I calculated genetic diversity and linkage disequilibrium (LD) along the pseudoautosomal region (PAR) of the Z chromosome using population genomics data of ostrich. In contrast to theoretical expectation, levels of diversity on the PAR were not significantly higher close to the sex-determining region (SDR) compared to autosomal values. Additionally, I observed a lower level of LD on the PAR compared to the average for the Z chromosome and no significant level of LD across the PAR boundary was detected, indicating recombination allows the boundary-proximal region of PAR to behave independently of SDR. Considered together with a higher level of recombination rate in females in the proximity of the SDR, this observation might help explain the maintenance of a long PAR in ostriches and other ratites. Altogether, the results of this thesis make a modest contribution to our understanding of sex chromosome evolution in birds.
sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2019. s. 51
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1788
Emneord
sex chromosomes, female heterogamety, recombination suppression, genetic map, inversions, genetic diversity, pseudoautosomal region
HSV kategori
Forskningsprogram
Biologi med inriktning mot evolutionär genetik
Identifikatorer
urn:nbn:se:uu:diva-379665 (URN)978-91-513-0612-4 (ISBN)
Disputas
2019-05-20, Lindahlsalen, Evolutionsbiologiskt centrum, Norbyvägen 18A, Uppsala, 13:00 (engelsk)
Opponent
Veileder
2019-04-232019-03-252019-06-18