Recombinant DNA technology, or DNA cloning, refers to the transfer of a DNA fragment from one organism to a self-replicating element such as a bacterial plasmid. The DNA fragment of interest can then be propagated in a foreign host cell. This type of technology was first used in the 1970s, and it has become a very common practice in molecular biology labs today.

Scientists that are studying a particular gene often use bacterial plasmids to create multiple copies of the gene. Plasmids are circular, self-replicating DNA molecules, distinct from the normal bacterial genome. Plasmids and other types of cloning vectors are also used by the Human Genome Project researchers as they generate enough identical material for further study.

More specifically, to clone a gene, isolate the DNA fragment that contains the gene of interest. This is done with restriction enzymes. Then join the gene with a plasmid that has been cut with the same restriction enzymes. The result is called a recombinant DNA molecule. After introduction into suitable host cells, the recombinant DNA is then reproduced along with the host cell DNA.


Plasmids can carry up to 20,000 bp of foreign DNA. Besides bacterial plasmids, some other cloning vectors include viruses, bacteria artificial chromosomes (BACs), and yeast artificial chromosomes (YACs). Cosmids are artificially constructed cloning vectors that carry up to 45 kb of foreign DNA and can be packaged in lambda phage particles for infection into E. coli cells. BACs utilize the naturally occurring F-factor plasmid found in E. coli to carry 100 to 300 kb DNA inserts. A YAC is a functional chromosome derived from yeast that can carry up to 1 MB of foreign DNA. Bacteria are most often used as the host cells for recombinant DNA molecules, but yeast and mammalian cells also are used.