Give an account of the Blue-White Method of selection of recombinants.

Blue – white method of selection of Recombinants:

The blue – white screen is a screening technique that allows for the rapid and convenient detection of recombinant bacteria in vector based molecular cloning experiments. This method is based upon the inspectional inactivation of the lac-z gene present on the vector. This gene expresses the enzyme b - galactosidase substrate called X – gal into blue colours product. If the lac –z gene is inactivated due to the presence of the insert, then enzymes is not expressed. Cells transformed with vectors containing recombinant DNA will produce white colonies; cells transformed with non-recombinant plasmids (i.e. only the vector) grow into blue colonies.

The Blue-White Method of selection of recombinants: Based on insertional inactivation the foreign gene is inserted into Lac Z gene coding for Beta-galactosidase enzyme which are used as selectable markers. The Betagalactosidase converts colourless substrate (X gel) into blue coloured product. In transformed hosts, Lac Z is activated due to insertion of foreign DNA. Nontransformed colonies convert colourless X gel (chromogenic substrate) into blue coloured product. The transformed colonies remain white or colourless. It helps to differentiate between transformant or recombinant and non-transformant or nonrecombinant.