In this method a recombinant DNA is inserted in the gene which inactivates the functioning of gene. Insertional inactivation is a efficient method to identify transformants.
Example:
Blue-white selection method: In this method, cloned DNA is inserted into the lac Z gene present on the vector. After insertion the lac Z gene is inactivated. The lac Z gene forms β−galactosidase enzyme which can break X-gal (a synthetic colourless substrate) into a blue coloured product. Thus, transformants will contain interrupted lac Z gene which will not produce β−galactosidase, appear in white colonies in the presence of X-gal.