What good will come from identifying genes if they have such small effect sizes? One answer is that it is possible to study pathways between each gene and behaviour. Even for genes with very small effect on behaviour, the road map is clearly marked for bottom-up analyses that begin with gene expression, although the roads quickly divide and become more difficult to follow to higher levels of analysis in the brain and the pathophysiology of behavioural disorders. Animal models will be increasingly important in bottom-up research that traces pathways from genes through the brain because of the powerful techniques available to investigate the effects of gene expression on the brain. Although animal models of behaviour are challenging, animal models will be especially valuable when it comes to understand how genes work from the bottom up through the brain. Even if there are many genes of small effect, each gene is a tiny window that offers a peek at the brain’s functioning. Moreover, looking through many of these windows simultaneously could lead to a systems approach to the brain because each
