Genetically engineered bacteria have been used in the commercial production of

Options

A. thyroxine
B. Testosterone
C. Human insulin
D. Melatonin

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the commercial production of substances using genetically engineered bacteria. We need to identify which of the given options is produced using this method.

2. **Identifying Genetically Engineered Bacteria**: Genetically engineered bacteria are created through recombinant DNA technology, where specific genes are inserted into bacteria to produce desired substances. A common example of such bacteria is *Escherichia coli* (E. coli).

3. **Analyzing the Options**:
- **Thyroxin**: This hormone is produced by the thyroid gland and is not typically produced using genetically engineered bacteria.
- **Testosterone**: This male sex hormone is produced by the testes and is also not produced using genetically engineered bacteria.
- **Human Insulin**: This is a hormone that regulates blood sugar levels and is produced using genetically engineered bacteria, specifically *E. coli*. The gene that codes for human insulin is inserted into the bacteria, allowing it to produce insulin on a large scale.
- **Melatonin**: This hormone is produced by the pineal gland and is not produced using genetically engineered bacteria.

4. **Conclusion**: Based on the analysis, the correct answer is **human insulin**, as it is the only substance listed that is commercially produced using genetically engineered bacteria.

### Final Answer:
Genetically engineered bacteria have been used in the commercial production of **human insulin**.

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