Most participants’ DNA (N = 343) was obtained at age 16 using Oragene™ DNA kits (Genetek, Calgary, AB, Canada), 45 participants were genotyped using blood drawn at age 19. Genotype at the 5-HTTLPR was determined for each sample as described previously (Bradley, Dodelzon, Sandhu, & Philibert, 2005). Consistent with prior research (Brody et al., 2009), we treated genetic variation at the 5-HTTLPR as a dichotomous variable, 1 for those carrying at least one copy of the short allele and 0 for those homozygous for the long allele. Among the 388 respondents, 5.4% were homozygous for the short allele (ss), 33.8% were heterozygous (sl), and 60.8% were homozygous for the long allele (ll). Using the Hardy-Weinberg equilibrium test, the observed distribution of 5-HTTLPR did not differ significantly from that predicted on the basis of simple Mendelian inheritance.
