What is blue-white screening and how does it work?

Blue-white screening is a method for identifying recombinant clones. Vectors contain the lacZ gene encoding beta-galactosidase, with an MCS within the coding region. When DNA is inserted into the MCS, it disrupts lacZ, preventing functional enzyme production. Cells are plated on media containing IPTG (inducer) and X-gal (chromogenic substrate). Cells with intact lacZ produce blue colonies (X-gal cleaved to blue product), while cells with inserts produce white colonies (no functional enzyme). This provides visual identification of potentially positive clones without additional screening steps.