Behavior is a property of a whole organism and functions at the level of the individual. Genes code for proteins and function at the molecular level. A gene does not code for a single behavioral phenotype in the whole organism, or even for a component of a behavioral phenotype or specific psychological process. An additional complexity is introduced because the molecular activities of many genes are regulated by features of the external environment or by behavior itself. The specific features of the environment that are most effective in modulating gene activity will, of course, depend on the specific gene and in most cases are presently unknown.
Gene products are part of an integrated metabolic system.
There may be need for a battery of behavioral tests. Although several good proposals have been made, there is currently no widely accepted battery of behavioral tests covering the range of behavioral endpoints important for the understanding of human disease. Individual tests exist for certain functions, but these differ in many details among laboratories. It is important that a comprehensive battery be constructed with the aid of well established methods of psychological testing. On the other hand, standardization would presume that tests of psychological constructs are well-developed .