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 of which component is NOT absolutely necessary for a plasmid to function as a cloning vector, we will analyze each option provided:

1. **Ori (Origin of Replication)**:
- The Ori is essential for the replication of the plasmid within a host cell. Without this site, the plasmid cannot replicate, meaning it cannot be passed on to daughter cells during cell division. Therefore, the Ori is absolutely necessary.

2. **High Copy Number**:
- High copy number refers to the ability of a plasmid to replicate many times within a host cell, producing numerous copies of itself. While having a high copy number can be beneficial for obtaining large quantities of the plasmid, it is not strictly necessary for the plasmid to function as a cloning vector. A plasmid can still be effective with a low or medium copy number. Thus, this characteristic is NOT absolutely necessary.

3. **Selectable Marker**:
- A selectable marker is crucial for distinguishing between cells that have taken up the plasmid (transformants) and those that have not (non-transformants). This allows researchers to identify and isolate successful transformations. Therefore, a selectable marker is absolutely necessary for the cloning process.

4. **Cloning Site**:
- The cloning site is where the gene of interest is inserted into the plasmid. Without this site, the plasmid cannot accommodate the foreign DNA. Thus, the cloning site is also absolutely necessary.

Based on this analysis, the component that is NOT absolutely necessary for a plasmid to function as a cloning vector is:

**Answer: High Copy Number**