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:
“Mozart has the classic purity of light and the blue ocean; Beethoven the romantic grandeur which belongs to the storms of air and sea, and while the soul of Mozart seems to dwell on the ethereal peaks of Olympus, that of Beethoven climbs shuddering the storm-beaten sides of a Sinai. Blessed be they both! Each represents a moment of the ideal life, each does us good. Our love is due to both.”
—Henri-Frédéric Amiel (1821–1881)
“The white man regards the universe as a gigantic machine hurtling through time and space to its final destruction: individuals in it are but tiny organisms with private lives that lead to private deaths: personal power, success and fame are the absolute measures of values, the things to live for. This outlook on life divides the universe into a host of individual little entities which cannot help being in constant conflict thereby hastening the approach of the hour of their final destruction.”
—Policy statement, 1944, of the Youth League of the African National Congress. pt. 2, ch. 4, Fatima Meer, Higher than Hope (1988)
“Historians will have to face the fact that natural selection determined the evolution of cultures in the same manner as it did that of species.”
—Konrad Lorenz (1903–1989)