There are many DRD4 alleles and genotypes, and how to analyze them varies somewhat. Most methods revolve around separating the two most common alleles (4- and 7-repeat) into separate groups based largely on the work of Asghari et al. (1995), who showed the 7-repeat allele functions more poorly than the 4-repeat allele. One method is to collapse the alleles into short (≤ 5 repeats) and long (6 or more), but it is not clear that the number of repeats is directly related to function (Wong, Buckle, & Van Tol, 2000). With this issue in mind, and given that there is evidence that the third most common allele (2-repeats) functions similarly to the 4-repeat allele (Schoots & Van Tol, 2003), we chose to follow what is common in the literature related to DST, in which variation in the DRD4 variable is studied as the presence or absence of 7 repeats of a 48 base pair sequence (i.e. 7− vs. 7+). The 7+ variant is associated with decreased neuronal dopamine signaling and thus provides a potential functional link between genetics and behaviors
