plasmid

noun

Etymology: From plasma + -id, coined by American molecular biologist Joshua Lederberg in 1952.

1. A loop of double-stranded DNA that is separate from — and replicates independently of — the chromosomes; such loops are most commonly found in bacteria, but they are also sometimes found in archaeans and eukaryotic cells, and they are used in genetic engineering as a vector for gene transfer.

   “These discussions have left a plethora of terms adrift: pangenes, bioblasts, plasmagenes, plastogenes, chondriogenes, cytogenes and proviruses, which have lost their original utility owing to the accretion of vague or contradictory connotations. At the risk of adding to this list, I propose plasmid as a generic term for any extrachromosomal hereditary determinant.”

   “This is how the F (for "fertility") plasmid, which forms the basis of a lot of classical E. coli genetics, is transferred from one cell to another.”