Plasmid:A circle ofDNAthat is self-replicating (autonomously replicating) and distinct from the normalgenomeofbacteria. Aplasmidcontainsgenesthat as a rule are notessentialto the growth or survival of thecell. Some plasmids can integrate into thehostgenome, can be artificially constructedinthelaboratory,作为cloningvectors (carriers). "Asectionof the wormgene插入一个质粒, a structure for carrying genes into bacteria." (New York Times, Jan 16, 2003)
