AP BIOLOGY

Detailed explanation-1: -The vector is then inserted into a competent host cell viable for transformation, which are then grown in the presence of X-gal . 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.

Detailed explanation-2: -Assertion: : Insertion of recombinant DNA within the coding sequence of beta-galactosidase results in colourless colonies. Reason: Presence of insert results in inactivation of enzyme beta-galactosidase known as insertional inactivation.

Detailed explanation-3: -The colonies formed by non-recombinant cells, therefore appear blue in color while the recombinant ones appear white. The desired recombinant colonies can be easily picked and cultured. Isopropyl -D-1-thiogalactopyranoside (IPTG) is used along with X-gal for blue-white screening.

Detailed explanation-4: -Cells containing recombinant plasmids can often be identified as containing recombinant plasmids by screening for the insertional inactivation of a second genetic marker on the plasmid.

Detailed explanation-5: -Bacteria carrying recombinant plasmids therefore form white colonies. To screen bacterial colonies, the chromogenic substrate X-Gal and the gratuitous inducer IPTG are mixed with suitable dilution of a culture, combined with molten top agar, and then spread on agar plates containing the appropriate antibiotic.