Youths’ DNA was obtained using Oragene™ DNA kits (Genetek; Calgary, Alberta, Canada). Youths rinsed their mouths with tap water, then deposited 4 ml of saliva in the Oragene sample vial. The vial was sealed, inverted, and shipped via courier to a central laboratory in Iowa City, where samples were prepared according to the manufacturer’s specifications. Genotype at DRD4 was determined for each youth as described by Lichter et al. (1993). Genotype at the 5-HTTLPR was determined for each sample as described previously (Bradley, Dodelzon, Sandhu, & Philibert, 2005). Genotype was then called by two individuals blind to study hypotheses or other information about the participants.
