a circular,double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA. Plasmids are most often found in bacteria and are used in recombinant DNA research to transfer genes between cells

• 质粒在细胞中能独立于染色体DNA而复制的圆形的，双链的DNA单元质粒大多常发现于细菌中，在DNA重组体研究中用来在细胞间传递基因