Future Directions for Behavior Genetics

Abstract

The Handbook has been organized into (1) an introduction; (2) quantitative methods and models in behavior genetics; (3) genetics of cognition; (4) genetics of personality; (5) genetics of psychopathology; and (6) conclusion. The Handbook has selected 33 current topics and issues in behavior genetics. Twenty-four studies of human behaviors and nine studies of animal models have been presented. Directions for future research on the selected topics have been highlighted in each chapter. Complex disorders or traits that have been presented here are polygenic and multifactorial, and thus they are influenced by both genes and environment, as well as by interactions between these two factors, and probably epigenetic factors that regulate the expression of implicated genes (a field still in its infancy). The quantitative genetic approaches using twin, adoption, or family studies determine the influences of genetic and environmental factors (a2, d2, c2, and e2) on the behaviors of interest. For most disorders or traits discussed in the Handbook, MZ twins almost always show higher correlations than DZ twins, suggesting that there is some genetic influence on the traits. However, the presence of the discordant MZ co-twins of probands with the disorders indicates that (1) non-shared environment is important; (2) unique environment can differentially influence expression of the same genes that the co-twins share; (3) multiple genes, interaction of the genes, and/or interaction of genes and environment play roles in the development of the traits; and (4) epigenetic factors not yet identified play a role in masking gene expression. This list suggests that (1) future research in behavior genetics will be enhanced by studying non-shared environmental sources of variation; (2) there is a need to identify more genes directly involved in the behavior with the advance in molecular genetics; (3) interactions between genes and environment, as well as gene-environment correlation, are to be further explored;