Screening: Example of The Blue/white Selection
Many general purpose vectors such as pUC19 usually include a system for detecting the presence of a cloned DNA fragment, based on the loss of an easily scored phenotype. The most widely used is the gene coding for E. coli β-galactosidase, whose integrity can easily be detected by the ability of the enzyme it encodes to hydrolyze the soluble, colourless substrate X-gal (5-bromo-4-chloro-3-indolyl-beta-d-galactoside) into an insoluble, blue product (5,5'-dibromo-4,4'-dichloro indigo). Cloning a fragment of DNA within the vector-based gene encoding the β-galactosidase prevents the production of an active enzyme. If X-gal is included in the selective agar plates, transformant colonies are generally blue in the case of a vector with no inserted DNA and white in the case of a vector containing a fragment of cloned DNA.
Read more about this topic: Cloning Vector
Famous quotes containing the words blue, white and/or selection:
“Down the blue night the unending columns press
In noiseless tumult, break and wave and flow,”
—Rupert Brooke (1887–1915)
“The puritanical potentialities of science have never been forecast. If it evolves a body of organized rites, and is established as a religion, hierarchically organized, things more than anything else will be done in the name of “decency.” The coarse fumes of tobacco and liquors, the consequent tainting of the breath and staining of white fingers and teeth, which is so offensive to many women, will be the first things attended to.”
—Wyndham Lewis (1882–1957)
“It is the highest and most legitimate pride of an Englishman to have the letters M.P. written after his name. No selection from the alphabet, no doctorship, no fellowship, be it of ever so learned or royal a society, no knightship,—not though it be of the Garter,—confers so fair an honour.”
—Anthony Trollope (1815–1882)