Genetic Contributions to the Expression of Traits

This chapter provides an overview of genetic and molecular processes involved in the inheritance and expression of cognitive and behavioral traits, including intellectual and developmental disabilities. Chromosomes, the structures that house genes, are described, and an overview of some important terminology and mechanisms involved in gene expression is provided. Mendel’s work with single gene traits is overlaid onto our current understanding of the segregation and assortment of chromosomes into gametes. Conditions resulting from large chromosomal abnormalities and smaller scale mutations are discussed. Mechanisms underlying the inheritance and expression of traits and conditions attributable to single genes are contrasted with those of quantitative traits, which result from complex interactions between multiple genes and the environment. The chapter concludes with an overview of approaches used to identify genetic contributions to behavior.