Which of the following is not true for cloning vector

Options

A. more than two origin site of replication
B. vector should have selectable marker gene
C. single recognition site for the commonly used restriction enzyme
D. pBR-322 have tetracycline resistance

Answer

To determine which statement is not true for a cloning vector, let's analyze each option step by step:

1. **Understanding Cloning Vectors**: Cloning vectors are segments of DNA used to carry foreign DNA into a host cell. They must possess certain characteristics to function effectively.

2. **Option Analysis**:
- **Option A: More than two origin sites of replication**: This statement is not true. A cloning vector typically has only one origin of replication (ORI). Having more than one would complicate the replication process and is not a standard feature of cloning vectors.
- **Option B: Vector should have selectable marker genes**: This statement is true. Cloning vectors must have selectable marker genes to differentiate between recombinant and non-recombinant cells, allowing for the identification of successful transformations.
- **Option C: Single recognition site for commonly used restriction enzyme**: This statement is also true. Cloning vectors generally have a single recognition site for restriction enzymes to facilitate the insertion of foreign DNA without confusion between recombinant and non-recombinant forms.
- **Option D: PBR322 has tetracycline resistance**: This statement is true. PBR322 is a well-known cloning vector that contains antibiotic resistance genes, including one for tetracycline.

3. **Conclusion**: The only statement that is not true regarding cloning vectors is **Option A: More than two origin sites of replication**.

### Final Answer:
The statement that is not true for cloning vectors is **Option A: More than two origin sites of replication**.