Transgenesis

Transgenesis is the process of introducing an exogenous gene — called a transgene — into a living organism so that the organism will exhibit a new property and transmit that property to its offspring. Transgenesis can be facilitated by liposomes, plasmid vectors, viral vectors, pronuclear injection, protoplast fusion, and ballistic DNA injection.

Transgenic organisms are able to express foreign genes because the genetic code is similar for all organisms. This means that a specific DNA sequence will code for the same protein in all organisms. Due to this similarity in protein sequence, scientists can cut DNA at these common protein points and add other genes. An example of this is the "super mice" of the 1980s. These mice were able to produce the human protein tPA to treat blood clots.

Using plasmids from bacteria

The most common type of transgenesis research is done with bacteria and viruses which are able to replicate foreign DNA. The plasmid DNA is cut using restriction enzymes, while the DNA to be copied is also cut with the same restriction enzyme, producing complementary sticky-ends. This allows the foreign DNA to hybridise with the plasmid DNA and be sealed by DNA ligase enzyme, creating a genetic code not normally found in nature. Altered DNA is inserted into plasmids for replication.