单词	plasmid
释义	plasmid /ˈplazmɪd / noun Biology A genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium or protozoan. Plasmids are much used in the laboratory manipulation of genes. Compare with episome.The bacterium contains a plasmid, a circular piece of DNA that holds the gene and promoter sequence.... The replication control genes of bacterial plasmids face selection at two conflicting levels. We note, however, that few if any of the genes borne by bacterial plasmids are under strong positive selection at all times. Origin 1950s: from plasma + -id2.
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