D4DR

D4DR is a human gene, located on chromosome 11. It is (so far) one of the only genes proven to be directly linked to a human personality trait. When the D4DR gene is mutated or elongated, studies have shown that the individual may be more interested in danger, excitement and thrill seeking.

Gene expression
The gene is active in the regulation of dopamine, a neurotransmitter that (among other things) mediates pleasure and emotion. Research on the precise effects of the D4DR gene is still inconclusive, but cells with an elongated copy of this gene appear to react more strongly to dopamine molecules.

Studies
In two studies published in Nature Genetics, subjects filled out personality questionnaires and had blood taken for genetic analysis. The scientists found that those whose answers showed them to be exploratory and excitable &mdash; two hallmarks of novelty-seeking &mdash; also possessed a longer version of D4DR, compared with those who are more reserved and reflective. A few other studies have replicated these results (including two done in Japan) but at least one has found no such correlation. In any case, thrill-seeking behavior is probably mediated by several genes, and the variance attributable to D4DR by itself is not particularly large.