Genetic engineering is the manipulation of DNA to produce genes with desired characteristics, such as correction of a mutation or increased production of a particular protein.

In order to work with the DNA easily, the desired gene is first cloned, or cut out of the chromosome and placed into a small, easily managed, piece of DNA known as a vector. Vectors may be viruses, which infect cells and replicate inside them, or plasmids, which can also replicate inside cells, but do not leave the cell and infect new cells.

Genes are cloned in two steps:

1) The vector and chromosome are cut into fragments by restriction endonucleases. These enzymes cut DNA at specific recognition sequences.

2) The DNA fragments are joined together by the enzyme DNA ligase.

The resulting DNA molecules are known as recombinant DNA, combining DNA from two different sources.