Which of the following is a cloning vector?

Options

A. cosmid
B. Phagemid
C. plasmid
D. All of these

Answer

To determine which of the options is a cloning vector, we need to understand what a cloning vector is. A cloning vector is a DNA molecule used to carry foreign DNA into a host cell for replication and expression. Here’s a step-by-step breakdown of the options provided:

1. **Understanding Cloning Vectors**:
- Cloning vectors are DNA molecules that can carry foreign DNA into a host organism. They are essential tools in genetic engineering and molecular biology.

2. **Analyzing the Options**:
- **Option 1: Cosmid**:
- A cosmid is a hybrid vector derived from a bacteriophage lambda and a plasmid. It can carry larger fragments of DNA (up to 45 kb) and is used for cloning in bacteria. Thus, cosmid is indeed a cloning vector.
- **Option 2: Phagemid**:
- A phagemid is a type of plasmid that contains a phage origin of replication. It can also be used for cloning purposes and is considered a cloning vector as it allows for the insertion of foreign DNA and its propagation in host cells.
- **Option 3: Plasmid**:
- Plasmids are small, circular, double-stranded DNA molecules that can replicate independently of chromosomal DNA. They are widely used as cloning vectors due to their ability to carry foreign DNA and replicate within bacterial cells.

3. **Conclusion**:
- All the options mentioned (cosmid, phagemid, and plasmid) are types of cloning vectors. Therefore, the correct answer is that all of these are cloning vectors.

### Final Answer:
All of the options (cosmid, phagemid, and plasmid) are cloning vectors.