GENETIC AND ENVIRONMENTAL-INFLUENCES ON COGNITION DURING CHILDHOOD

The basic methodology of behavior genetics is described in the context of the twin and sibling/adoption design. Results of applying this mod el to cross-sectional data on cognitive development throughout the lif espan are presented. Results from a large longitudinal twin and adopti on study of general intelligence are presented to illustrate the use o f the basic behavior genetic model in studying the causes of continuit y and change in development. A special model is presented for the stud y of abnormal behavior occurring at the extremes of the distribution a nd an adaptation of the model is discussed for the study of genetic li nkage or the mapping of quantitative trait loci (QTL). Results of appl ying this model to a sample of twins and kindred siblings indicated th e presence of a major QTL for dyslexia on chromosome 6. The purpose of the paper is to illustrate the scope of behavior genetic methodology in studying individual differences in behavior in a biosocial context.