Transgenic animals
Transgenic animals carry and express a foreign gene; over 95% are mice. They model diseases, make proteins in milk (like Rosie the cow) and test vaccine safety.
What 'transgenic' means
A transgenic animal has had its DNA changed so that it possesses and expresses an extra (foreign) gene. Transgenic rats, rabbits, pigs, sheep, cows and fish have been made, but over 95% of all existing transgenic animals are mice.
How a transgenic animal is made, in outline
- The chosen gene is joined to suitable DNA so it can be expressed.
- It is put into a fertilised egg or early embryo, usually by micro-injection into the nucleus.
- The embryo is placed in a surrogate mother to develop.
- Offspring are tested; those carrying and expressing the gene are bred.
Why transgenic animals are made
| Use | What it means | Example |
|---|---|---|
| Normal physiology and development | Study how genes are regulated and how they affect body functions and growth | Genes that alter insulin-like growth factor, to learn its role |
| Study of disease | Animals made as models of human diseases, to try new treatments | Models for cancer, cystic fibrosis, rheumatoid arthritis, Alzheimer's |
| Biological products | Animals make costly human proteins used as medicines | α-1-antitrypsin for emphysema; attempts for PKU and cystic fibrosis; Rosie's milk |
| Vaccine safety | Test vaccines before they are used on humans | Transgenic mice for polio vaccine; could replace monkeys |
| Chemical safety testing | Animals made more sensitive to toxic substances, so toxicity tests give results faster | Testing the toxicity of drugs and chemicals |
Rosie, the first transgenic cow
In 1997, Rosie became the first transgenic cow. Her milk was enriched with a human protein, 2.4 grams per litre. It contained human alpha-lactalbumin and was nutritionally more balanced for human babies than natural cow milk.
Rosie's milk was designed to be closer to human breast milk for babies. Every new medicine and vaccine sold in India must pass safety tests, and transgenic mice can make such tests faster and more reliable.
5 marks: “What are transgenic animals? Explain five reasons for producing them, with an example of each.” Animals with a foreign gene they express; over 95% are mice. Normal physiology (insulin-like growth factor); disease models (cancer, cystic fibrosis, Alzheimer's); biological products (α-1-antitrypsin, Rosie); vaccine safety (polio vaccine on mice); chemical safety testing (toxicity).
2 marks: “What was special about Rosie? Why was her milk better for human babies?” First transgenic cow (1997). Her milk had human alpha-lactalbumin (2.4 g per litre of human protein), making it nutritionally more balanced for babies than normal cow milk.
1 marks: “Name the human protein produced in transgenic animals to treat emphysema.” α-1-antitrypsin.
Transgenic uses: Please Don't Bother Very Cute mice: Physiology, Disease models, Biological products, Vaccine safety, Chemical safety.