Exogenous DNA is deoxyribonucleic acid, which originates outside of the organism of concern or study. The introduction of exogenous DNA into a cell is called transfection. This can be a natural process, as occurs when a virus infects cells. Transfection can also be done artificially. The commonly used DNA transfection methods are (a) chemical methods, including calcium phosphate precipitation, DEAE-dextran complexation and lipid-mediated DNA transfer; (b) physical methods, including electroporation, microinjection, and biolistic particle delivery (gene gun); and (c) using recombinant, lab manipulated viruses as vectors.

The process by which cells take up exogenous DNA from the surrounding medium is called transformation. The discovery of transformation dates back to 1928, when Frederick Griffith, by inducing pneumonia in mice exposed to viable and encapsulated Streptococcus pneumoniae, provided evidence that DNA was genetic material. Oswald Theodore Avery and colleagues provided proof of this concept in 1944. They demonstrated that purified...