Chapter 19 Solutions Manual Study Guide Questions And Correct Answers

32. 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 how the geneticist can identify bacteria that contain a copy of a plasmid with the foreign DNA. {Ans: Solution: The geneticist should plate the bacteria on agar medium containing penicillin to select for cells that have taken up the plasmid. The medium should also have X-gal and an inducer of the lac operon, such as IPTG or even lactose. Cells that have taken up a plasmid without foreign DNA will have an intact lacZ gene, produce functional β- galactosidase, and cleave X-gal to make a blue dye. These colonies will turn blue. In contrast, cells that have taken up a plasmid containing a foreign DNA inserted into the lacZ gene will be unable to make functional β-galactosidase. These colonies will be white.}*look at #43 in solutions manual* {Ans: Yee}5. After DNA fragments have been separated by gel electrophoresis, how can they be visualized? {Ans: Solution: DNA molecules can be