Animals can also be genetically engineered. The process is more complex than for bacteria because animals are multicellular and the gene must be inserted at the right early stage of development to end up in every cell of the adult.
Transgenic animals producing proteins for medicine
One major use of transgenic animals is producing useful proteins in their milk:
- The gene for a useful human protein (e.g. a blood-clotting factor) is inserted into the DNA of a fertilised animal egg, typically a goat, sheep or cow.
- The egg is implanted into a surrogate mother and develops normally into an animal that carries the gene.
- The animal grows up and starts producing milk. The human protein is secreted into the milk along with normal milk proteins.
- The milk is collected and the human protein is purified out.
This approach can make proteins that are too large or complex for bacteria to produce. It has been used to make:
- Alpha-1-antitrypsin (used to treat a rare lung disorder)
- Human blood-clotting factors for haemophilia patients
- Antithrombin (used during surgery to prevent dangerous clots)
The animals live normal lives; they are just very expensive milk producers.
Other uses of transgenic animals
- GM mice are widely used in medical research. Specific human disease genes can be put into mice so that researchers can study the disease and test possible treatments.
- Transgenic fish have been engineered to grow faster (e.g. AquAdvantage salmon, approved in the USA and Canada).
- GM mosquitoes carrying a "self-limiting" gene have been released in some areas to try to suppress mosquito populations that spread diseases like dengue and Zika.