Genetic linkage and candidate gene association studies on personality have yielded mixed results. Linkage studies test for coinheritance of genetic markers and traits within families. There have been various linkage findings for the different personality scales, including Neuroticism (Kuo, et al., 2007; Neale, Sullivan, & Kendler, 2005; Wray, et al., 2008), Harm Avoidance (Cloninger, et al., 1998), Novelty Seeking (Curtis, 2004), Psychoticism and Extraversion (Gillespie, et al., 2008), but none have been consistently replicated. Candidate gene association studies test for a correlation in the population between scores on a personality scale and a specific genetic variant with a known function that could relate to personality. The two most extensively studied candidate genes are the dopamine D4 receptor gene DRD4 and serotonin transporter gene SLC6A4. Several studies have found association between a variant of the dopamine D4 receptor gene and Novelty Seeking (Benjamin, et al., 1996; Ebstein, Nemanov, Klotz, Gritsenko, & Belmaker, 1997; Ebstein, et al., 1996), and between a polymorphism (5-HTTLPR) in the promoter region of the serotonin transporter gene and anxiety-related traits like Harm Avoidance (Lesch, et al., 1996;
