Study of heredity in general and of genes in particular. Modern genetics began in the 19th century with the work of Gregor Mendel, who formulated the basic concepts of heredity. In 1909 the word gene was coined by Wilhelm Johannsen, thus giving genetics its name. In the same year, Thomas Hunt Morgan provided evidence that genes occur on chromosomes and that adjacent genes on the same chromosome form linkage groups. This led to the important discovery that genes affect molecular action at the cell level, as evidenced by human hereditary diseases such as inborn errors of metabolism. Molecular genetics began in earnest in the 1940s when Oswald Avery showed that DNA is the chromosome component that carries genetic information. The molecular structure of DNA was deduced by James D. Watson, Francis Crick, and Maurice Wilkins. These and other developments led to the deciphering of the genetic code of the DNA molecule, which in turn made possible the recombination techniques of genetic engineering, discovered in the 1970s. An understanding of genetics is necessary for the diagnosis, prevention, and treatment of hereditary diseases, the selective breeding of plants and animals, and the development of industrial processes that use microorganisms. See also behaviour genetics; biotechnology.

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