Schissel, Ann2015-10-132015-10-132015-04https://hdl.handle.net/11299/174889University of Minnesota Ph.D. dissertation. April 2015. Major: Psychology. Advisor: Monica Luciana. 1 computer file (PDF); vii, 84 pages.Serotonin (5-HT) has a demonstrated influence on several aspects of the human experience including personality, behavior, and psychopathology. One aspect of the 5- HT system that has received considerable attention in research concerns individual differences in the 5-HT transporter promoter region polymorphism (5-HTTLPR) and their associations with behavior. A well-researched component of the 5-HTTLPR literature focuses on the potential interactions between 5-HTTLPR genotype and adverse life events on the development of Major Depressive Disorder (MDD). The validity of this interaction, however, has been questioned due to inconsistent findings. The current project is an attempt to replicate the 5-HTTLPR by environment interaction in a large epidemiological sample, while also examining some of the proposed reasons for inconsistent findings. Results consistently suggest stressful life events (SLE) are related to the development of MDD; however, main effects of 5-HTTLPR and the interactions between 5-HTTLPR variants and SLE on the development of MDD are non-significant. Potential reasons for these negative findings, as well as limitations of this current project, are discussed.en5-HTTLPRThesis or Dissertation