This topic was visited briefly in the thread, Genetic Effects on Personality, but I was surprised not to find more on it. (Is there a taboo I don't know about? What's the ethical stance on this nowadays?)
(An answer in that thread mentions serotonin receptor genetics specifically as having strong links to personality, but provides no explicit references.)
The question: What links have been measured between genotypes and personality outcomes within personality frameworks/models like the Big Five?