Suppose a scientist wants to clone the gene for human insulin. He uses a plasmid

Question

Suppose a scientist wants to clone the gene for human insulin. He uses a plasmid that contains the lacZ gene, an origin of replication, and an ampicillin resistant gene. He inserts the human insulin gene into a restriction site located within the lacZ gene. Then he transforms this plasmid into bacteria without a functional lacZ gene and spread the appropriate dilution onto bacterial plates. When the product of the lacZ gene, beta-galactosidase, interacts with the subtrate X-Gal on LB agar, colonies turn blue. Which of the plates below indicates the human insulin gene was successfully inserted in the plasmid?

Explanation / Answer

The presence of intact Lac Z gene results in the formation of beta-galactosidase that hydrolysis X gal to form blue colour. Therefore, it means that the colonies that contain intact Lac Z gene will appear as blue colonies on agar plate containing ampillicin. In contrast, when insulin gene is inserted within Lac Z gene, Lac Z gene is disrupted so that it no longer produces beta-galactosidase. Therefore, the colonies containing insulin gene within the X- gal gene will fail to hydrolyse X-gal and they would appear as white colonies on agar plate containing ampillicin.

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