Genetic engineering can be defined as the science dealing with the correction of nature's mistake at the level of hereditary unit, the DNA and to improve the quality of organism for purposes by implanting desired genes.

Genes are specific parts of DNA. For cloning specific gene, it must be separated from the DNA and then it should be attached with a vector like plasmid or bacteriophage DNA (vector are carriers). As the plasmid or the bacteriophage DNA multiplies within the bacteria or the bacteriophages the gene inserted in them also multiplies. For this purpose, the following methods are applied.

(i) At first the plasmids DNA found in bacteria are brought out of the bacterial cell by lysing the bacterial cell. The plasmid which is used to carry the gene to be cloned is also called passenger or vehicle DNA or Vector. In place plasmid, bacteriophage DNA can also be isolated and used as vector.

(ii) In the next step, the gene to be isolated and cloned is identified in the DNA of another bacteria or organism and is bought out.

(iii) Now using an enzyme called restriction endonuclease the specific part of the DNA carrying the specific gene is cut out. With the same enzyme the specific part of the plasmid where the gene will fit is opened by cut and the equivalent part of the plasmid iş taken out so that the inserted gene fits will in the plasmid. The cut end of the plasm and the DNA well have sticky ends in one of their single strand. These sticky ends help them to join with their complementary parts.