In vitro multiplication of gene of interest is done through

Polymerase chain reaction is in vitro method for amplification of gene of interest. Gel electrophoresis separates the DNA fragments formed due to restriction digestion. Southern blotting identifies the DNA fragment with desired sequence from a group different DNA fragments with diverse sequences. Bioreactors are used for large scale production of recombinant protein or desired product by growing genetically engineered organisms or its cells  in providing optimal conditions.