Genetic engineering is that branch of biotechnology. This is a process in which the alteration of the genetic makeup of cells is done by deliberate and artificial means. This process involves transfer or replacement of genes to create recombinant DNA. This can be done by cutting DNA molecules at specific sites to get fragments containing desirable and useful genes from one type of cell. Thereafter, these genes can be inserted into a suitable carrier or vector. Now, the recombinant DNA can be put into a foreign cell of a bacterium or plant or animal cell.

By this technique they acquire useful characteristics, such as disease resistance or to make useful enzymes, hormones, vaccines, etc.

The three tools for recombinant DNA technology are as follows :

1. Cell culture containing cells with the desired DNA segment (gene).

2. DNA modifying enzymes such as (a) Restriction endonuclease from various bacteria (b) DNA ligase from Escherichia coli which joins DNA molecules (c) DNA polymerase from E. coli.

3. Cloning vectors. The desired gene is inserted in the vectors or gene carrier to form DNA.