In recombinant DNA technology, the term vector refers to

Options

A. the enzyme that cuts DNA into restriction fragments
B. the sticky end of a DNA fragment
C. a plasmid used to transfer DNA into a living cell
D. a DNA fragment which carries only ori gene

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the term "vector" in the context of recombinant DNA technology. We need to identify which of the provided options correctly defines what a vector is.

2. **Analyzing the Options**:
- **Option 1**: "The enzyme that cuts DNA into restriction fragments."
- This option is incorrect because the enzyme that performs this function is called a restriction enzyme, not a vector.

- **Option 2**: "The sticky ends of DNA fragment."
- This option is also incorrect. Sticky ends refer to the overhanging ends of DNA that are generated after cutting with restriction enzymes, not a vector.

- **Option 3**: "A plasmid used to transfer DNA into living cells."
- This option is correct. In recombinant DNA technology, a vector is indeed a plasmid or another type of DNA molecule that is used to carry foreign DNA into a host cell.

- **Option 4**: "A DNA fragment which carries only origin."
- This option is incorrect as well. While the origin of replication is important for DNA replication, a vector typically carries more than just the origin; it also carries the foreign DNA.

3. **Conclusion**: Based on the analysis of the options, the correct answer is **Option 3**: "A plasmid used to transfer DNA into living cells."

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