Comparisons of Sex Determining Pathways Across Caenorhabditis Species

  • Author / Creator
    Reidy, Keith
  • Biological pathways have the ability to tolerate mutations and evolve to control novel traits. Selection pressures act on these pathways playing a key role in the evolution and divergence of species. Sex determination in Caenorhabditis nematodes is a rapidly evolving trait which can provide insights into how biological pathways can be modified from a common set of ancestral genes. C. elegans and C. briggsae are two of three androdioecious species within the Elegans group of the Caenorhabditis genus. These two species are both morphologically and developmentally similar but their genetic control of hermaphroditism is different. XX animals in these species are somatically female but are capable of producing and storing sperm before switching to oocyte production. Genetic screens have been used to isolate mutants which disrupt the C. briggsae sex determining pathway, the results of which have identified orthologs of the C. elegans sex determining genes. Regulation of spermatogenesis differs in C. elegans and C. briggsae; C. elegans fem mutants are females whereas C. briggsae fem mutants are hermaphrodites. Identification of the molecular lesion in the fem mutants isolated from these screens have been useful for determining the functional domains of these important proteins. In the same genetic screen that identified the Cbr-fem mutants, three mutants were isolated which appeared to be novel members of the C. briggsae sex determining pathway. These mutants display phenotypes not seen in C. elegans. Whole genome sequencing followed by mapping has revealed that one of these appears to be a gain of function tra-1 allele, one of them appears to be a weak hypomorph of fem-3 and the third one does not contain a mutation in any known sex determining gene. The current candidate for this mutant is the kinase, pink-1. C. briggsae has a closely related sister species which uses a male/female sex determining system. Comparisons between sex determination gene orthologs in these two species show greater than ninety percent identity at the amino acid level. Sex determining genes that were known to be present in C. briggsae but not in C. elegans were also found in C. nigoni so their presence alone is not enough to facilitate hermaphroditism in C. briggsae.

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  • Graduation date
  • Type of Item
  • Degree
    Master of Science
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  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
  • Specialization
    • Molecular Biology and Genetics
  • Supervisor / co-supervisor and their department(s)
  • Examining committee members and their departments
    • McDermid, Heather (Biological Sciences)
    • Srayko, Martin (Biological Sciences)
    • Wevrick, Rachel (Medical Genetics)