The replica plate method is used in genetic engineering for identifying transformed bacterial cells (cells containing foreign DNA). Only some of the cells transformed with a specific DNA may actually have foreign DNA. Thus, it is essential to screen those cells having foreign DNA by the technique of colony hybridisation (only for bacterial cells) figure. A similar technique named plaque hybridisation is used for screening transformed bacteriophages.

The principle of colony hybridisation involves in-situ hybridisation of transformed bacterial cells with a radioactive probe sequence. Due to the specificity of probe, a single colony can be rapidly identified (through radioactivity) amongst thousand of colonies.