Insertional Inactivation of an antibiotic resistance gene and then identifying the recombinants by setting the plates of both antibiotics tetracycline and ampicillin is a very complex process. Thus alternate selectable markers are used on the basis of color-producing ability in chromogenic substances. In plasmid pUC19 a gene lacz is present. It encodes for the production of the beta-galactosidase enzyme. This enzyme leads to the development of a blue color colony in the chromogenic substance when it is active. A foreign gene is inserted in the site of this lacz gene thus deactivating it. Now the recombinant organism will not produce beta-galactosidase enzyme as a result and no blue color colony is seen. and white colonies are developed. Thus due to this color difference transformants and non-transformants can be identified.