Function of 'ori' site in a vector is to

Options

A. Initiate insertional inactivation
B. Initiate replication
C. Codes for the proteins involved in replication of the plasmid
D. Initiate antibiotic resistance

Answer

### Step-by-Step Solution

1. **Understanding the Vector**: A vector is a vehicle used to carry foreign DNA into a host cell. It is essential for cloning and gene transfer.

2. **Identifying the 'ori' Site**: The 'ori' site stands for "origin of replication." It is a specific sequence of nucleotides in the vector that is crucial for the replication of the vector itself.

3. **Function of the 'ori' Site**: The primary function of the 'ori' site is to initiate replication. This means that when the vector is introduced into a host cell, the 'ori' site allows the vector to replicate independently, creating multiple copies of the foreign DNA it carries.

4. **Importance of Replication**: The ability to replicate is vital because it ensures that as the host cell divides, it also replicates the vector along with the foreign DNA. This leads to the production of many copies of the desired gene or DNA sequence.

5. **Evaluating the Options**:
- **Option A**: Initiate insertional inactivation - Incorrect, this relates to the selectable marker, not the 'ori'.
- **Option B**: Initiate replication - Correct, this is the primary function of the 'ori' site.
- **Option C**: Codes for proteins involved in replication of the plasmid - Incorrect, the 'ori' does not code for proteins; it is a sequence that facilitates replication.
- **Option D**: Initiate antibiotic resistance - Incorrect, this is a feature of selectable markers, not the 'ori'.

6. **Conclusion**: The correct answer is that the function of the 'ori' site in a vector is to **initiate replication**.