| dc.description.abstract | An analysis of over 10,000 plant genome sizes (GSs) indicates that most species have smaller genomes than expected given the incidence of polyploidy in their ancestries, suggesting selection for genome downsizing. Given the estimated rate of DNA loss following polyploidy is likely to be very low, we focused on the role of double-strand break (DSB) repair pathways may have played. In this thesis, I analysed i) GS reconstruction for the exploration of GS rate changes since the last polyploidy event in a species lineage; 2) identification of orthologs and linear modelling to examine how the characteristics and activities of genes of DNA repair pathways influence GS; 3) expression pattern analysis in diploid-polyploid Gossypium complexes to whether determine young polyploids exhibit higher gene expression levels of DNA repair and recombination genes, and how these levels change with polyploid age. GS diversity in angiosperms is characterized by widespread genome downsizing after polyploidy and occasional upsizing as seen in the plant order Poales. In addition, GS tends to decrease with increasing age of polyploids, and this reduction accelerates at higher chromosomal ploidy levels. In the potential genome downsizing related DNA repair and recombination involved genes, the gene copy numbers decrease with an increase in polyploid age, particular the Ku70-Ku80 heterodimer showing a significant interactive effect leading to genome downsizing. Expression analysis suggests that genes associated with HR contribute to genome downsizing in early polyploids, likely by removing LTR retrotransposons, as opposed to increased c-NHEJ activity that would lead to a higher frequency of indels. | en_US |
