Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


Ken Hillers


Meiosis is a specialized form of cell division in sexually reproducing eukaryotes. Crossovers are physical connections formed between homologous chromosomes during meiosis; these connections help ensure normal segregation of homologous chromosomes at meiosis I. However, the yeast Saccharomyces cerevisiae and other eukaryotes can still segregate homologs properly even in the absence of some crossovers. This is due to a backup mechanism known as distributive segregation, which correctly segregates non-crossover chromosomes at a higher rate than if segregation were completely random. To study distributive segregation, we have generated diploid yeast with one homeologous chromosome pair consisting of a Saccharomyces cerevisiae chromosome V and a Saccharomyces carlsbergensis chromosome V. This pair of chromosomes rarely recombine resulting in crossing over occurring in less than 3% of meiosis. Appropriate segregation of this chromosome pair during meiosis will depend on distributive segregation; we can then assess the possible roles of candidate proteins in distributive segregation through determination of the effect of mutation on segregation of this chromosome pair. Our work has focused on the roles of three proteins, Ndj1, Tid1, and Spo16. These three proteins affect meiosis in many ways, including the efficiency of crossover regulation and the overall timing of meiosis, but their roles during distributive segregation are not fully known.

A comparison of spore viability among WT, ndj1, and tid1 strains reveals an elevated incidence of 2-spore-viable tetrads (suggestive of chromosome nondisjunction) in ndj1, but not tid1; these results suggest that the Ndj1 protein, but not the Tid1 protein, plays some role in distributive segregation. spo16 strains seem to also show elevated levels of 2-spore-viable tetrads, but due to a lack of data no deductions can be made about the role of Spo16 in distributive segregation.

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