Botany · Ch 9 — Biotechnology and Its Applications
Transgenic Animals
Transgenic Animals
Why Transgenic Animals Matter
A transgenic animal is one whose genome has been deliberately altered by introducing a foreign gene, called a transgene. The key point is that this change is stable and heritable — the foreign DNA becomes a permanent part of the animal's genetic material and is passed on to its offspring.
Transgenic rats, rabbits, pigs, sheep, cows, and fish have all been produced, but by far the most common transgenic animal is the mouse — over 95 per cent of all existing transgenic animals are mice.
How Transgenic Animals Are Made
The textbook does not detail the laboratory steps here, but it is important to understand the principle: a gene from one species (say, a human gene for a therapeutic protein) is inserted into the fertilised egg or early embryo of the host animal. The embryo is then implanted into a surrogate mother. When the offspring is born, every cell in its body — including its germ cells — carries the transgene. That is why the trait is inherited.
Why Create Transgenic Animals? Five Major Purposes
The book lists five specific reasons, each with a clear example.
1. To study normal physiology and development
Transgenic animals let scientists watch, in a living body, exactly how a gene is regulated and how it affects normal body function and development. A commonly studied example is insulin-like growth factor — by introducing genes from other species that alter how this growth factor is produced, and then studying the resulting biological effects, researchers learn about the factor's real role in the body, something far harder to investigate directly in humans for ethical reasons.
2. To study disease
This is one of the most valuable uses. By inserting a gene that causes a human disease (like cancer, cystic fibrosis, rheumatoid arthritis, or Alzheimer's) into a mouse, researchers create a model of that disease. They can then study how the disease progresses, what genes or environmental factors influence it, and — crucially — test potential treatments before trying them on humans.
3. To produce biological products
Some medicines needed to treat human diseases rely on biological products that are otherwise expensive to manufacture. The textbook's example is alpha-1-antitrypsin, a human protein used to treat emphysema; similar attempts are being made to develop treatments for phenylketonuria (PKU) and cystic fibrosis this way.
In 1997, the first transgenic cow, named Rosie, produced human protein-enriched milk at a rate of 2.4 grams per litre. Rosie's milk contained the human protein alpha-lactalbumin, making it more nutritionally balanced for human babies than ordinary cow's milk.
4. To test vaccine safety
Transgenic mice are being developed for use in testing the safety of vaccines before they are used on humans. For example, transgenic mice are being used to test the safety of the polio vaccine. If this approach proves successful and reliable, it could replace the current practice of using monkeys to test the safety of vaccine batches.
5. To test chemical safety (toxicity testing)
This is also known as toxicity or safety testing, and the procedure is the same as that used to test the toxicity of drugs. Transgenic animals are engineered to carry genes that make them more sensitive to toxic substances than ordinary, non-transgenic animals. They are then exposed to the substance being tested and the effects are studied. Because these animals react more strongly, toxicity results can be obtained in less time.
Common Misconception
Do not confuse transgenic animals with cloned animals. A clone is a genetic copy of an existing animal (like Dolly the sheep). A transgenic animal has a new gene added — it is not a copy of any pre-existing individual. Some animals can be both (e.g., a cloned transgenic sheep), but the concepts are distinct.
Summary Table of Uses
| Purpose | What it achieves | Textbook example |
|---|---|---| …