The Crabtree (CT) effect is a metabolic phenomenon where yeast perform aerobic fermentation of glucose to ethanol in glucose- and oxygen-rich environments, rather than the expected metabolism of aerobic respiration. Yeast that prefer to ferment in aerobic, high glucose conditions are called CT positive, and yeast species that prefer to respire are called CT negative. Although we know what genes control the onset of the CT effect, how these genes affect metabolism to initiate this response is still unclear. We are utilizing metabolomics analysis to study the CT effect by exploring how individual genes affect yeast fermentation and respiration. Metabolomics allows us to track the changes of individual metabolites that are involved the chemical reactions of metabolism. We are interested in exploring how the deletion of genes involved in the CT effect affect the fermentative and respiratory metabolism of CT-positive and -negative yeast. With this information, we will be able to compare the differences between CT-positive and -negative yeast to better understand how they may have evolved. This project can also aid in a more targeted approached to metabolically engineer these different species for optimal ethanol production. Lastly, this project can provide us with new insights on the CT effect that may be applicable to other organisms, such as cancer, that share a similar metabolism to CT positive yeast.