Genetics is the study of genes and the variation of characteristics that are influenced by genes—including physical and psychological characteristics. All human traits, from one's height to one's fear of heights, are driven by a complex interplay between the expression of inherited genes and feedback from the environment.
Many genes interact to influence the human brain. Almost all normal and disordered characteristics are polygenic, meaning that they are each shaped by a large number of genes.
Scientists are tasked with a massive but increasingly plausible mission: mapping the pathway from one's genes to the person one sees in the mirror. What they learn about the power of genes has implications for understanding mental illness and psychological differences between individuals, as well as the psychological effects of non-genetic factors.