Plasmids replicate to produce many plasmid molecules in each host bacterial cell. The number of copies of each plasmid in a bacterial cell is determined by the replication origin, which is the position within the plasmid molecule where DNA replication is initiated. Most binary vectors have a higher number of plasmid copies when they replicate in E. coli; however, the plasmid copy-number is usually lower when the plasmid is resident within Agrobacterium tumefaciens.
Plasmids can also be replicated using the polymerase chain reaction (PCR).