The evolution and expression of Drosophila meiosis genes

Drosophila melanogaster is unique amongst model organisms in that males utilize achiasmatic meiosis, where formation of the synaptonemal complex (SC) and recombination are absent. Most organisms require the SC and chiasmata for the successful completion of meiosis and production of viable gametes, making D. melanogaster an ideal system for the study of meiotic variation. Drosophila are not the only species of dipterans (true flies) that possess male achiasmatic meiosis. Evidence for males with chiasmatic or achiasmatic meiosis is dispersed throughout the order Diptera and data for many species is lacking. The goal of my research was to examine in detail the origin and evolution of male achiasmatic meiosis in Diptera. This was done in three parts: 1) assessing the presence and absence of meiosis genes across dipteran species, 2) analyzing the rate of evolution of Drosophila achiasmatic meiosis genes, and 3) evaluating differences in expression and splicing of meiosis genes between D. melanogaster males and females. I queried genome and transcriptome data from eleven dipteran species, spanning the breadth of the dipteran clade, for both genes involved in canonical meiosis and D. melanogaster achiasmatic meiosis. I found that six meiosisspecific genes were lost prior to the gain of Drosophila male achiasmy genes. This suggests that either changes in meiosis occurred or other novel genes arose to compensate for the loss of these meiosis genes and perhaps this facilitated the later evolution of Drosophila male achiasmatic meiosis. To assess the evolution of fourteen Drosophila achiasmatic meiosis genes, I performed phylogenetic, rate, selection and co-evolution analyses. My results show that, although these genes appear to be evolving under purifying selection at the whole gene level, they are all evolving rapidly compared to their paralogs and paralogous genes throughout the Drosophila genome. I also found evidence of significantly similar rates of evolution across several Drosophila species for two groups of male meiosis genes. This indicates that the genes within each group are