Why are plasmids used as vectors in genetic engineering?

Plasmids possess several key features that make genetic engineering more productive.

• Plasmids are extra-chromosomal, which makes it easier to introduce foreign DNA into a cell than integrating DNA into chromosome.
• Plasmids are self-replicating, driven by an origin-of-replication.
• Plasmids are small in size, making it easy to work with and transform into their host.
• Plasmids usually contain antibiotic resistance genes, enabling the selection for transformed hosts.