Question

A geneticist uses a plasmid for cloning that has the lacZ gene and an ampicillin resistance gene. She uses molecular biology techniques to first insert her gene of interest into the cloning plasmids, then to transform the plasmids into bacterial cells.   She screens for recombinant bacteria with her gene of interest by growing them on Petri dishes supplemented with ampicillin and X-gal.

On the Petri dish, both blue and white colonies grow. The recombinant colonies of interest to the geneticist should be                            [ Select ]                       ["white", "blue", "something else"]         .

Answer 1

this is called blue-white screening, the plasmid has Beta-galactosidase gene and ampicillin resistance gene, the gene of interest is inserted into the beta-galactosidase gene in the plasmid, functional beta-galactosidase enzyme coded by the beta-galactosidase gene converts X-gal to a blue pigment if the gene of interest is inserted to the beta-galactosidase gene inactivates beta-galactosidase gene, so the X-gal cannot be converted to blue pigment, so colony formed from non- recombinant cells appears blue it has functional lac Z ( beta-galactosidase) gene, and colonies formed from recombinant cells appears white.

so the answer is a) white.