In rDNA technology, probes are used for

A probe is single stranded DNA or RNA tagged with radioactive isotope and whose sequence is complementary to the sequence of gene insert in the recombinant transformant and can hydrogen bond with it. Where ever it binds to the DNA of a colony, one can understand that it is colony with recombinant transformants. It is used in the selection of recombinants in the method of colony hybridization.