This study finds that three polymorphisms in three dopaminergic genes (DAT1, DRD2, and DRD4) predict academic achievement among a sample of adolescents. The dopaminergic system has been found to affect attention, motivation, memory, and reward, and the authors hypothesize that behavior problems associated with the genes impair learning. On the other hand, the impact of the genes is weak, making findings hard to replicate.
I should note that the multivariate model includes race and gender, and the effect of race on grades remains when genes are entered into the equation. In fact, the impact of race is stronger than the three genes together.