Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Molecular Genetics and Genomics


English (en)

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Barak A Cohen


A complex trait is one that exhibits continuous phenotypic variation due to genetic variation in many quantitative trait genes: QTGs). The ultimate goal of genetics is to relate genotype to phenotype; in the case of complex traits this requires a better understanding of what types of genes harbor causal natural variation, and what form the variation takes. Here I describe two experiments using the model complex trait of sporulation efficiency in the yeast Saccharomyces cerevisiae, one to specifically investigate how small effects contribute to a quantitative trait and the other to determine whether certain types of genes are more likely to be QTGs. A previous study showed that four quantitative trait nucleotides: QTNs) in three transcription factors: TFs) are responsible for approximately 80% of the differences in sporulation efficiency between a high sporulating oak tree isolate and a low sporulating vineyard isolate. To determine the character of the remaining causal variation, I fixed these four QTN as both oak and vineyard variants. I found small effect quantitative trait loci: QTL) were physically linked to and have extensive genetic interactions with the large effect QTN. To test whether QTGs are predictable I identified sporulation efficiency QTL in two additional vineyard isolates, and found that while new QTGs included kinases as well as TFs, all QTGs act at the decision point in the sporulation pathway. I conclude that small and large effect QTL interact to create complex phenotypes and that causal variation is concentrated at crucial pathway bottlenecks.


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