Transformation is a process in which a cell takes up and functionally integrates exogenous DNA. There are many examples of natural transformation between bacteria, virus and bacteria, bacteria and plants, or virus and eukaryotic cells. Genetic engineering techniques are artificial adaptations of cases of natural transforming systems.
The process of transformation was initially described by Fred Griffith (1877–1941) in 1928 (Griffith 1928). The experiments on the transformation of pneumococcal bacteria, published in 1944 by T. Oswald Avery (1877–1955), Colin MacLeod (1909–1972), and Maclyn McCarty (1911–2005), established that the genetic information is chemically written in DNA (Avery et al. 1944).