Figure 1 shows the location of the SNPs exhibiting interactions in the CDP sample. The interaction effects are largely clustered in the central block of the gene. Figure 2 plots the regression lines for the interaction effect for the SNPs that interacted significantly with parental monitoring. Across the three SNPs in Figure 2, there was a stronger association between genotype and externalizing behavior with decreased parental monitoring. The regression lines for all three SNPs also cross over: The genotype associated with the highest levels of externalizing behavior at the low end of parental monitoring in each case was associated with the lowest levels of externalizing behavior at the extreme high end of parental monitoring. However, the confidence intervals at the environmental ends of the distribution were large and overlapping; accordingly, the mean differences in externalizing behavior across genotypes were nonsignificant at either end. Thus, there was insufficient power to conclude that the genotypic effects exhibited significant crossing over.
