We described the experiments aimed at testing the hypothesis that the influence of some genes on personality traits is due to their influence on neurocognitive differences. For instance, it was proposed that MAOA and DBH genes affect the individual differences in Consciousness because of their influence on executive functions. However, the results showed that DBH gene is associated only with the variability of executive functions and that MAOA gene - with personality traits linked to Agreeableness. Moreover, the executive functions can mediate the influence of MAOA on these traits. We proposed that one of the possible psychological mechanisms, which mediates the influence of MAOA on Agreeableness, is disposition to reinforce socially encouraged forms of behaviors.