[1] Exogenous DNA can be found naturally in the form of partially degraded fragments left over from dead cells.
[6] In 1928, bacteriologist Fredrick Griffith observed exogenous DNA alongside bacterial transformation in the species Streptococcus pneumoniae.
Repeated experiments proved exogenous DNA integration was possible in other species of bacteria, prompting studies to extend to mammal cells.
These treatments typically involve making the targeted cell membrane more permeable towards accepting exogenous DNA, one such example being exposing the bacteria to a calcium ion solution, or a mixture of polyethylene glycol and dimethylsulfoxide.
[10] Another treatment method is the utilization of electricity (electroporation or electro transformation) to create holes in the cell membrane for the DNA to enter.
[14] Viral methods (or transduction) use recombinant, lab manipulated viruses as vectors to alter embryos and sperm cells.
[17] For example, transgenic farm animals can produce human pharmaceuticals alongside increased milk or meat production.
Epididymal sperm cells were shown to react to exogenous nucleic acids, allowing for DNA to reversibly bind to the spermatozoa through ionic interactions.
[19] The ability of sperm cells to locate and internalize exogenous DNA was then used to transfer foreign genes into an oocyte during fertilization to create transgenic animals.