WHAT DOES THE GENOME DO?
Our genome is solely responsible for many of our traits. These include physical traits such as eye and hair color and ear lobe shape. Our genome is also responsible for affecting behavior and complex diseases such as depression, autism, and schizophrenia. It also affects how we interact with our environment—everything from our sensitivity to air pollution to how we react to alcohol intake and how well we derive nutrition from certain foods. For example, most of the adult world population cannot digest milk because the gene encoding the critical protein for digesting milk (lactase) is normally turned off post weaning. The exception is certain northern European populations and some other groups that do not turn off the lactase gene and thus can typically digest milk throughout their lives. Finally, our genome affects our susceptibility to particular diseases.
The example of lactose intolerance due to lactase insufficiency is an example of a trait due to variation in a single gene (a monogenic trait). Many traits are multigenic, that is, they are determined by the interaction of the products of many genes. Determining the genetic cause of a monogenic trait is relatively easy; determining the genetic basis for a multigenic trait is more complicated. Finally, many traits are influenced not only by an individual’s genome but also by his or her environment; that is, traits may have both a genetic component and an environmental component.