Youths’ DNA was obtained using Oragene™ DNA kits (Genetek; Calgary, Alberta, Canada). Youth 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 5HTTLPR was determined for each youth as previously described (18). Of the sample, 6.4% were homozygous for the short allele (ss), 35.2% were heterozygous (sl), and 58.4% were homozygous for the long allele (ll). None of the alleles deviated from Hardy-Weinberg equilibrium (p = .77, ns). Consistent with prior research (19), genotyping results were used to form two groups of participants: those homozygous for the long allele and those with either 1 or 2 copies of the short allele.
