Transgenic animals have been used:

Options

A. For testing sefety of vaccines
B. For testing toxicity of drugs
C. To produce useful biological products
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding Transgenic Animals**: Transgenic animals are those that have had their genomes altered by the transfer of a gene or genes from another species or breed. This genetic modification allows them to express new traits or produce specific products.

2. **Testing the Safety of Vaccines**: Transgenic animals can be used as models for human diseases. They can be engineered to express human receptors, making them suitable for testing the safety and efficacy of vaccines intended for human use. This allows researchers to observe how these vaccines interact with human-like biological systems.

3. **Testing the Toxicity of Drugs**: Transgenic animals are also valuable in pharmacology for testing the toxicity of drugs. By using these animals, researchers can assess how a drug affects a living organism that closely mimics human biology, which is crucial for understanding potential side effects before human trials.

4. **Producing Useful Biological Products**: Transgenic animals can be engineered to produce valuable biological products, such as proteins and antibodies. For example, transgenic mice can be created to produce human antibodies, which are essential for various therapeutic applications. Additionally, other transgenic animals like cows and sheep can be modified to produce milk containing therapeutic proteins.

5. **Conclusion**: Given the roles of transgenic animals in vaccine testing, drug toxicity testing, and the production of useful biological products, the correct answer to the question is that transgenic animals have been used for all of the above purposes.

**Final Answer**: Transgenic animals have been used for testing the safety of vaccines, testing the toxicity of drugs, and producing useful biological products. Therefore, the answer is all of the above.

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