While twin-studies can help to elucidate the extent to which an observed behavior is heritable, genomic research approaches can begin to identify chromosomal regions or specific genes associated with the behavioral phenotype (e.g., nicotine withdrawal). To date, linkage studies using smoking- related phenotypes have included behaviors such as smoking initiation (Bergen et al., 2003; Ehlers and Wilhelmsen, 2006; Morley et al., 2006; Vink et al., 2004), quantity smoked (Swan et al., 2006; Morley et al., 2006; Bergen et al., 1999; Duggirala et al., 1999; Goode et al., 2003; Li et al., 2003; Li et al., 2006; Saccone et al., 2003; Wang et al., 2005), habitual smoking (Ehlers and Wilhelmsen, 2006; Bierut et al., 2004; Gelernter et al., 2004), nicotine dependence (FTND: Swan et al., 2006; Li et al., 2006; Gelernter et al., 2007; Straub et al., 1999; DSM-IV: Swan et al., 2006; Gelernter et al., 2007), short-term cessation (Swan et al., 2006), and maximum cigarettes smoked in a 24-hour period (Saccone et al., 2007a). Suggestive linkage has been reported at multiple locations across the genome, but with most LOD scores
