Stage 3: Cloning

The plasmids or viruses serve as vectors that can introduce the DNA fragments into cellsusually, but not always, bacteria (figure 5). As each cell

reproduces, it forms a clone of cells that all contain the fragment-bearing vector. Each clone is maintained separately, and all of them together constitute a clone library of the original source DNA.

Stages in a genetic engineering experiment. In stage 1, DNA containing the gene of interest (in this case, from an animal cell) and DNA from a plasmid are cleaved with the same restriction endonuclease. The genes amp^r and lacZ´ are contained within the plasmid and used for screening a clone (stage 4). In stage 2, the two cleaved sources of DNA are mixed together and pair at their sticky ends. In stage 3, the recombinant DNA is inserted into a bacterial cell, which reproduces and forms clones. In Stage 4, the bacterial clones will be screened for the gene of interest.