Background Information (Highlight 2 main ideas in the information.)In this day and age, it seems that genes are "everything" when it comes to determining the characteristics of an organism. However, the importance of the environment in biology cannot be denied. For example, nearly everyone knows that a dry season can ruin crop yields. However, digging a little deeper reveals even more intriguing examples of environmental influence on organisms. For instance, research has shown that the sex of some species of reptiles is influenced by the temperature at which the reptiles' eggs are incubated during development. This kind of observation presents an apparent paradox, because sex is usually regarded as being genetically—not environmentally—determined. Thus, there appear to be certain situations in which the environment affects not only the growth and health of an organism, but also the use or deployment of the organism's genes. Does this mean that genes aren't, in fact, everything? The observation that genetically identical organisms often vary greatly in phenotype clearly shows that gene-environment interaction is indeed an important regulator of phenotypic variation, including variation related to a number of diseases. In fact, the impact of environmental factors on disease etiology (or causation) has gained greater recognition in recent years. This has led to the conclusion that both genes and environment can affect disease—not just separately, but through direct interaction with each other. This relatively new attitude presents considerable challenges, as well as surprising benefits, for the study of human disease.