In recombinant DNA technique, the term vector refers to :

Options

A. plasmids that can transfer foreign DNA into a living cell
B. cosmids that can cut DNA at specific based sequence
C. plasmids that can join different DNA fragments
D. cosmids that can join different DNA fragments

Answer

**Step-by-Step Solution:**

1. **Understanding the Term "Vector":**
- In the context of recombinant DNA technology, a vector is a vehicle used to transfer foreign genetic material into another cell.

2. **Identifying the Correct Definition of Vector:**
- The options provided include:
- Plasmids that can transfer foreign DNA into a living cell.
- Cosmids that can cut DNA at specific base sequences.
- Plasmids that can join different DNA fragments.
- Cosmids that can join different DNA fragments.

3. **Analyzing Each Option:**
- **First Option:** Plasmids that can transfer foreign DNA into a living cell.
- This is correct because plasmids are commonly used as vectors in recombinant DNA technology to introduce foreign DNA into host cells.

- **Second Option:** Cosmids that can cut DNA at specific base sequences.
- This is incorrect. Cosmids are hybrid vectors but do not have the ability to cut DNA; this function is performed by restriction enzymes.

- **Third Option:** Plasmids that can join different DNA fragments.
- This is also incorrect. While plasmids can carry DNA, the actual joining of DNA fragments is done by the enzyme DNA ligase.

- **Fourth Option:** Cosmids that can join different DNA fragments.
- This option is incorrect for the same reason as the third; joining of DNA fragments is facilitated by DNA ligase.

4. **Conclusion:**
- The correct answer is **"plasmids that can transfer foreign DNA into a living cell."** This accurately describes the role of vectors in recombinant DNA technology.