Which vector can clone only a small fragment of DNA?

Options

A. Yeast artificial chromosome
B. Plasmid
C. Cosmid
D. Bacterial artificial chromosome

Answer

To determine which vector can clone only a small fragment of DNA, we need to analyze the cloning capacities of the given options: yeast artificial chromosome, plasmid, cosmid, and bacterial artificial chromosome.

### Step-by-Step Solution:

1. **Understand the Types of Vectors**:
- We need to identify the different types of vectors and their cloning capacities.

2. **Yeast Artificial Chromosome (YAC)**:
- YACs can clone large fragments of DNA, typically up to 1,000 kilobases (Kb). This makes them unsuitable for cloning small fragments.

3. **Plasmid**:
- Plasmids are small, circular DNA molecules found in bacteria. They can typically clone DNA fragments up to about 15 Kb. This is relatively small compared to other vectors.

4. **Cosmid**:
- Cosmids can clone DNA fragments ranging from 35 to 50 Kb. This is larger than what plasmids can accommodate, thus not suitable for small fragments.

5. **Bacterial Artificial Chromosome (BAC)**:
- BACs can clone larger DNA fragments, typically up to 195 Kb. Again, this is not suitable for small fragments.

6. **Conclusion**:
- Among the options provided, plasmids have the smallest cloning capacity, allowing them to clone DNA fragments up to 15 Kb. Therefore, the vector that can clone only a small fragment of DNA is the **plasmid**.

### Final Answer:
The vector that can clone only a small fragment of DNA is the **plasmid**.