Re: Key features of a plasmid?

A plasmid is a piece of DNA that can replicate itself. Thus, minimally, a
plasmid is a piece of DNA that has an "origin of replication". This is a
region of DNA that can attract the DNA replication machinery of the cell.
Almost always, there are genes on the plasmid that confer some sort of
advantage to the host cell. Common genes are those that confer antibiotic
resistance to the cell possessing the plasmid, however there are lots of
other genes that can be selected.