Micro-injection is a method used to

Options

A. 1) produce sticky ends of DNA
B. 2) provide protection against pathogen
C. 3) purify the DNA
D. 4) inject recombinant DNA into the nucleus of an animal cell.

Answer

### Step-by-Step Solution:

1. **Understanding Micro-injection**: Micro-injection is a technique used in molecular biology to introduce substances such as DNA, RNA, or proteins directly into the cells.

2. **Evaluating the Options**:
- **Option 1: Produce sticky ends of DNA**: This is incorrect. Sticky ends are generated using restriction endonucleases, not micro-injection.
- **Option 2: Provide protection against pathogens**: This option is also incorrect. Protection against pathogens is typically achieved through vaccinations, not through micro-injection.
- **Option 3: Purify the DNA**: This is incorrect as well. DNA purification is done through various biochemical methods, not micro-injection.
- **Option 4: Inject recombinant DNA into the nucleus of an animal cell**: This is the correct option. Micro-injection is specifically used to inject recombinant DNA into the nucleus of animal cells for genetic modification.

3. **Conclusion**: After evaluating all the options, the only correct use of micro-injection is to inject recombinant DNA into the nucleus of an animal cell.

### Final Answer:
Micro-injection is a method used to inject recombinant DNA into the nucleus of an animal cell. Therefore, the correct answer is **Option 4**.

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