In order to study the genetics of an organism, it is necessary that some kind of sexuality occurs in this organism. For long time, bacteria and viruses were believed to reproduce through purely asexual methods, so that these organisms did not make suitable material for genetic studies. In the year 1946, two American scientists, J. Lederberg and E.L. Tatum demonstrated sexuality in bacteria for the first time, and this opened a new area of research. For this and other contributions, Lederberg and Tatum shared with G.W. Beadle the Nobel Prize in medicine, for the year 1958.

Once sexuality in bacteria was established, short generation time and several other facilities which these organisms provided, made them very suitable materials for genetic studies. Many experiments which could not be conducted with higher organisms could be carried out with relatively great ease in bacteria. As a result of work on these organisms great advances have been made in the field of genetics in the last five decades. A brief account of basic genetics of these organisms will be presented in this section. For any detailed account, an advanced text book like "Sexuality and Genetics of Bacteria" written by F. Jacob and E.L. Wollman (1961) should be consulted.