Plasmids are suitable vectors for gene cloning because :

Options

A. these are small circular DNA molcules which can integrate with host chromosomal DNA
B. these are small circular DNA molecules w ith their own replication origin site
C. these can shuttle between prokaryotic and eukaryotic cells
D. these often carry antibiotic resistance genes

Answer

### Step-by-Step Solution:

1. **Definition of Plasmids**: Plasmids are small, circular, double-stranded DNA molecules that exist independently of chromosomal DNA in bacteria and some eukaryotes. They are extra-chromosomal and can replicate independently.

2. **Self-Replication**: One of the key features of plasmids is that they have their own origin of replication. This allows them to replicate independently within a host cell, making them ideal for gene cloning.

3. **Selectable Markers**: Plasmids often contain selectable markers, such as antibiotic resistance genes. This allows researchers to easily identify and select for cells that have successfully taken up the plasmid, as only those cells will survive in the presence of the antibiotic.

4. **Cloning Sites**: Plasmids typically have restriction sites where foreign DNA can be inserted. This allows for the easy incorporation of genes of interest into the plasmid.

5. **Integration with Host DNA**: While some vectors can integrate into the host genome, plasmids are primarily used for their ability to remain separate from chromosomal DNA, which is beneficial for cloning purposes.

6. **Shuttling Between Cells**: While some plasmids can be engineered to shuttle between prokaryotic and eukaryotic cells, this is not a general feature of all plasmids. The primary reason for their use as vectors is their ability to replicate independently.

7. **Conclusion**: The most accurate statement regarding why plasmids are suitable vectors for gene cloning is that they are small circular DNA molecules with their own replication origin site. This characteristic allows for the stable maintenance and replication of inserted foreign DNA.

### Final Answer:
Plasmids are suitable vectors for gene cloning because they are small circular DNA molecules with their own replication origin site.

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