ABSTRACT
Introduction Genetics is the scientific study of the inheritance of traits both physical and behavioural. Genes provide the assembly code for the molecules that make up life and enable reproduction of living organisms. Genes are located on chromosomes, which are highly folded and compressed linear molecules of deoxyribonucleic acid (DNA) housed in the nuclei of cells. They pass from generation to generation, providing familial resemblance and individual variation, which, through evolution, is responsible for the diversity of life. This chapter describes the basic principles of genetics and their relevance to psychiatric disorders. The first use of the term ‘genetics’ was in 1906 by the biologist William Bateson, but the science of genetics began much earlier. Gregor Mendel, a monk working in the monastery in Brno in 1866, described laws of inheritance based on his observations of the inheritance of seven simple bimodal traits in pea plants. Mendel suggested that each parent plant had a pair of units of inheritance for each trait but contributed only one unit from each pair to its offspring.
