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Faculty of Graduate Studies

Michael Clark

  • B.Sc. (University of California, Davis, 2020)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Genetic and Genomic Characteristics of a Selfish X Chromosome in Drosophila testacea

Department of Biology

Date & location

  • Friday, May 8, 2026
  • 1:00 P.M.
  • Elliott Building, Room 160

Examining Committee

Supervisory Committee

  • Dr. Steve Perlman, Department of Biology, University of Victoria (Supervisor)
  • Dr. Ryan Gawryluk, Department of Biology, UVic (Member)
  • Dr. Greg Owens, Department of Biology, UVic (Member)

External Examiner

  • Dr. Chris Nelson, Department of Biochemistry and Microbiology, UVic

Chair of Oral Examination

  • Dr. Andrew Wender, Department of Political Science, UVic

Abstract

Meiotic drivers are selfish genetic elements that manipulate the process of meiosis to increase their transmission, circumventing Mendel’s Law of equal segregation. Because meiosis fundamentally differs between the sexes, meiotic drivers use different mechanisms and strategies in male and female meiosis. While drivers in male meiosis use a strategy of killing meiotic products which don’t contain them, drivers in female meiosis will utilize a strategy of altering their segregation to ensuring a “winning” orientation. The mechanism that female meiotic drivers use to alter segregation is not well understood. For this thesis, I investigated a selfish X chromosome that causes both male and female meiotic drive in the woodland fly Drosophila testacea. In the first chapter, I provide an overview of meiotic drive, providing more background on the focus of my thesis, female meiotic drive. In the second chapter, I used controlled crosses to test whether one or two copies of this selfish X chromosome cause higher rates of nondisjunction, or chromosome segregation failure, in female flies. I found that females carrying one selfish X chromosome failed to transmit either of their X chromosomes at a significantly greater rate than wildtype females; this was even more pronounced in females with two selfish X chromosomes, creating a large number of sterile sons with an XO genotype. In contrast, females carrying two selfish X chromosomes almost never transmitted both of their X chromosomes. These results suggest that the two selfish X chromosomes interfere with each other over segregation in homozygous D. testacea females. Meiotic drivers tend to be structurally distinct from their non-driving counterparts, often containing chromosomal rearrangements like inversions or expansions of repetitive elements. In the third chapter, I analyze the selfish X chromosome for such structural differences, using Hi-C sequencing reads to generate chromosome-level scaffolds of the wildtype and driving X chromosomes. In doing so I demonstrate that the driving X chromosome has acquired an almost complete Wolbachia genome. Wolbachia are a group of intracellular bacteria symbionts found in insects and other terrestrial arthropods, notable for their ability to manipulate host reproduction to increase their transmission. Through comparisons with several Wolbachia genomes, I characterize the Wolbachia insertion and speculate on possible functions it may have. The work performed in my thesis helps to characterize some of the fascinating genetic and genomic characteristics of the selfish X chromosome, opening the door to further questions and research about female meiotic drive.

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