This is the interesting story on an SNP demonstrated (statistically significant) to influence behavior among white US citizens. The gene in question is OXTR and the effective SNP is rs53576.
People with two G alleles are more likely to seek emotional support if needed than people with one or two A alleles. But it's not just generic people... it is white undergraduate US-Americans, who may differ both culturally and genetically from other peoples.
For a change researchers did realize this problem and compared with a Korean sample. Koreans did not display this difference in behavior. So the allele behaves differently in US citizens of European ancestry than in Korean ones.
The question then became: is this ethnic difference caused by different cultural norms or different genetic pools or a combo of both. The answer would come from Korean-Americans: these behave almost identically to European-Americans and quite differently from Koreans in their home country. The result indicates that, while the allele induces a difference in behavior, the expression or blockade of this genetic expression is caused essentially by cultural norms: looking for emotional support is not favored in Korean culture and therefore Koreans raised at their homeland cannot not freely express this allele's push.
Culture hence shows that it can be dominant over genes. However that is not necessarily a good thing.
This is the summary on the allele's behavior recycled from Not Exactly Rocket Science, the reference paper being:
Heejung S. Kim et al., Culture, distress, and oxytocin receptor polymorphism (OXTR) interact to influence emotional support seeking. PNAS 2011. Open access.