a small cellular inclusion consisting of a ring of DNA that is not in a chromosome but is capable of autonomous replication
"The researcher isolated the plasmid from the bacteria to insert a gene for antibiotic resistance into its circular DNA."
A loop of double-stranded DNA that is separate from and replicates independently of the chromosomes, most commonly found in bacteria, but also in archaeans and eukaryotic cells, and used in genetic engineering as a vector for gene transfer.
"Scientists inserted the antibiotic resistance gene into a bacterial plasmid to create an effective vector for transferring traits between different strains."