Which of these is NOT absolutely necessary

Options

A. Ori
B. High copy number
C. Selectable marker
D. Cloning sites

Answer

To solve the question "Which of these is NOT absolutely necessary?" regarding the features of vectors in cloning, we will analyze each option provided:

### Step-by-Step Solution:

1. **Understanding the Features of Vectors**:
- Vectors are essential tools in molecular biology used for cloning DNA. They typically contain several important features that facilitate the cloning process.

2. **Identifying the Features**:
- **ORI (Origin of Replication)**: This is crucial as it is the site where replication begins. Without it, the vector cannot replicate within the host cell.
- **Selectable Marker**: This feature allows for the identification of successfully transformed cells. It helps in distinguishing between cells that have taken up the vector and those that have not. This is important for ensuring that only the desired recombinant cells are selected.
- **Cloning Site**: This is where the foreign DNA is inserted. It is essential for the actual process of cloning, as it provides a specific location for the DNA to be integrated into the vector.
- **High Copy Number**: This feature allows for the replication of multiple copies of the vector within the host cell. While it is beneficial for increasing the yield of cloned DNA, it is not absolutely necessary for the cloning process itself.

3. **Determining the Least Necessary Feature**:
- Among the features listed, the **High Copy Number** is the least critical for the basic function of a vector. While it enhances the efficiency of cloning by producing more copies, it is not required for the cloning to occur.

4. **Conclusion**:
- Therefore, the feature that is NOT absolutely necessary for a vector is the **High Copy Number**.

### Final Answer:
The correct option is **High Copy Number**.

---