An extrachromosomal genetic element consisting generally of a circular duplex of DNA which can replicate independently of chromosomal DNA. R-plasmids are responsible for the mutual transfer of antibiotic resistance among microbes. Plasmids are used as vectors for cloning DNA in bacteria or yeast host cells.
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 162 (