Multiple genetic methodologies have been employed to investigate the underlying genetic architecture of alcohol use and broader externalizing behaviors, including linkage analyses, candidate gene association studies and genome-wide association studies (GWAS) (Dick et al., 2015; Saccone et al., 1999; Treutlein and Rietschel, 2011; Wang et al., 2005). Linkage studies look within families to ascertain genomic regions traveling within affected (but not unaffected) family members (Hirschhorn and Daly, 2005). Looking across the genome, linkage studies allow for an unbiased interrogation. While successful in locating loci underlying traits that follow patterns of Mendelian inheritance, linkage has been much less successful for complex traits involving numerous genes and environmental influences, though there are ways in which this method can still be useful, particularly in the analysis of whole-genome sequence data (Ott et al., 2015). Association studies have become far more widely used as a statistically more robust method for complex phenotypes (Risch and Merikangas, 1996). Association studies test for genomic variants with statistically different frequencies in affected versus unaffected persons. Association analyses can be conducted within families (in which case one is testing
