Blue white screening

Blue white screening- Foriegn DNA and plasmid Dna are cut with restriction enzyme. Plasmid has gene for lactose hydrolysis lac z gene which codes for enzyme (β-galactosidase). Foriegn dna insert into lacz gene to form the recombinant. The recombinant dna is then transfered into a host cell , which are then grown in the presence of X-gal. 

Result-
colonies with an insert-containing plasmid have a non-functional β-galactosidase, and remain the whitish-cream color of standard E. coli. On the other hand, intact β-galactosidase ( non recombinant plasmid )produces pigment from x-gal (included in the transformation plate medium), turning the bacterial colony blue.

                                                
Imagehttps://en.wikipedia.org/wiki/Blue_white_screen



                                                                                                                                                                                                                                                                                                                                                            Imagesourcehttp://www.slideshare.net/tejondaru/blue-white-selectionpresentation

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