Question

Assume that one conducted a typical cloning experiment using pUC18, transformed an appropriate host bacterial strain (one carrying the lacZ complementing region), and plated the bacteria on an appropriate X-gal medium. Blue and white colonies appeared. Which of the two types of colonies, blue or white, would most likely contain the recombinant pUC18? Explain your answer.

Answer 1

Answer:

The pUC18 refers to a polylinker that is featured by enhanced multiple restriction locations. The enhanced number of restriction sites would upsurge the chance of the target DNA sequence being presented into the plasmid. If the sequence of the DNA is administered efficiently and obstructs the sequence of the LacZ gene in the restriction site, the bacteria will not be able to generate B galactosidase that cleaves X-gal.  

When the X-gal in the medium does not get cleaved, the colonies become white. In case, if the DNA was not effectively presented into the host DNA and the LacZ gene can generate B galactosidase, X-gal will get cleaved and the colonies will be blue.  

As the white colonies will be the hosts comprising the recombinant DNA, and pUC18 enhances the chance of DNA getting inserted, the white colonies will most probably comprise the recombinant pUC18.