Copy Number Variation, Stabilizing Selection, and Parasitism in Chilodonella uncinata



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Chilodonella uncinata is a unicellular eukaryotic species that has two nuclei within each cell: the micronucleus and macronucleus. The macronucleus is the center of cellular transcription but the genome is degraded during rounds of sexual conjugation. The macronuclear genome consists of many copies of single-gene chromosomes that were derived from the micronuclear genome. The primary purpose of this thesis is to elucidate the macronuclear chromosome distribution during asexual division of the ciliate C. uncinata. It is hypothesized that the macronuclear chromosomes are randomly assorted during asexual division, called the amitotic model. This type of division is predicted to lead to copy number variation (CNV) within asexually dividing populations and potentially leads to loss of macronuclear chromosomes. Using quantitative PCR (qPCR), differential amplification of macronuclear chromosomes were confirmed. Using a single-cell culturing method, along with qPCR, macronuclear chromosome copy number was found to be maintained after ~278 generations. Stabilizing selection was determined to be capable of maintaining chromosome copy number in a simulated population of C. uncinata in accordance with amitosis and without a molecular mechanism of copy number control. Finally, previous research suggested that C. uncinata is a parasite of mosquito larvae, but this dissertation shows that C. uncinata was not found in larvae tissue and did not increase mortality of mosquito larvae.



Genomics, Experimental evolution, Simulations, Stabilizing selection, Parasitism, Mosquitoes, Ciliate, Entomology