Question

A geneticist uses a plasmid for cloning that has the lacZ gene and a gene that confers resistance to penicillin. The geneticist inserts a piece of foreign DNA into a restriction site that is located within the lacZ gene and uses the plasmid to transform bacteria. Explain the two things the geneticist can use to identify bacteria that contain a copy of a plasmid with the foreign DNA.

Answer 1

The geneticist can plate bacteria on an agar-nutrient medium containing penicillin, one inducer of the lac operon (e.g., lactose or IPTG) and X-Gal.

Step-by-step explanation:

Transformed cells can be selected by plating bacteria on a medium containing penicillin to select the cells that carry the plasmid. Moreover, lactose (or IPTG) is an inducer of the lac operon and thereby bacteria that have an intact copy of the lacZ gene will produce β-galactosidase which is then used to cleave X-Gal (a chromogenic substrate for β-galactosidase), thus giving a blue color to the colonies. Finally, bacteria containing the plasmid with the foreign DNA which are not able to produce β-galactosidase will remain white.