Genetics is the scientific study of heredity and variation. It is concerned with the similarities and differences between individual organisms in the same species, and in different species. The characteristics of an individual organism are largely the result of information transmitted from the parent to the offspring, via the gametes (there is also an important environmental component). The understanding of how this occurs is the study of genetics.

Our growing knowledge of genetics is due to the work of many people, including Gregor Mendel, Edwin Chargaff, Oswald Avery, Thomas Morgan, George Beadle, Edward Tatum, James Watson and Francis Crick. The discoveries made by them and others have shown that inheritable characteristics are present in organisms in the form of genes. These genes are arranged on chromosomes made of DNA, except in the case of certain viruses that utilize RNA in place of DNA. Organisms that store chromosomes in...