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Comparisons of Sex Determining Pathways Across Caenorhabditis Species Open Access


Other title
C. nigoni
fem mutant
C. briggsae
Sex Determination
Type of item
Degree grantor
University of Alberta
Author or creator
Reidy, Keith
Supervisor and department
Pilgrim, David (Biological Sciences)
Examining committee member and department
McDermid, Heather (Biological Sciences)
Srayko, Martin (Biological Sciences)
Wevrick, Rachel (Medical Genetics)
Department of Biological Sciences
Molecular Biology and Genetics
Date accepted
Graduation date
Master of Science
Degree level
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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