The present research examined the interaction between genes and culture as potential determinants of individuals' locus of attention. As the serotonin (5-HT) system has been associated with attentional focus and the ability to adapt to changes in reinforcement, we examined the serotonin 1A receptor polymorphism (5-HTR1A). Koreans and European Americans were genotyped and reported their chronic locus of attention. There was a significant interaction between 5-HTR1A genotype and culture in the locus of attention. Koreans reported attending to the field more than European Americans, and this cultural difference was moderated by 5-HTR1A. There was a linear pattern such that those homozygous for the G allele, which is associated with reduced ability to adapt to changes in reinforcement, more strongly endorsed the culturally reinforced mode of thinking than those homozygous for the C allele, with those heterozygous in the middle. Our findings suggest that the same genetic predisposition can result in divergent psychological outcomes, depending on an individual's cultural context.