DNA was collected with QuickExtract buccal swabs and extracted with BuccalAmp solution as directed by the manufacturer (Epicenter). Subjects were instructed to rinse their mouths out with water before swabbing. DRD2 TaqI A was typed with a PCR/RFLP method [based on 88] described completely in Supplementary File S3. The DRD4 VNTR locus was genotyped using an adaptation of a previous protocol [89] described fully in Supplementary File 3. Allele frequency data was submitted to The Allele Frequency Database (ALFRED; http://alfred.med.yale.edu/alfred/sampleDescrip.aspsampleID001775)').
