Screening Recombinant DNA Libraries

A recombinant DNA library typically represents part or all of an organism’s genomic DNA or mRNA (represented as cDNA) cloned into vectors and stored as a collection of thousands of transformants. The construction of a complete library is only half the task; researchers then need to be able to identify the small number of clones bearing the DNA fragment of interest among the numerous transformants within the library. This process is called “screening a library” and it is the molecular equivalent of finding a needle in a haystack. Libraries may be screened by any one of several methods.