Question

You have isolated a DNA fragment containing a human gene involved in lung cancer and are working inserting it into a standard plasmid vector used in molecular cloning which has a multiple cloning site in the lacZ gene. After cutting the DNA fragment and the vector with the same restriction enzyme and ligating the cut DNA, you transform bacteria with hopefully the recombinant vector. How do you expect to identify bacteria with the recombinant vector?

	A.	Bacteria with the recombinant vector will be resistant to antibiotic treatment and form blue colonies in the presenceof X-gal.
	B.	Bacteria with the recombinant vector will be resistant to antibiotic treatment and form white colonies in the presenceof X-gal.
	C.	Bacteria with the recombinant vector will be sensitive to antibiotic treatment and form blue colonies in the presenceof X-gal.
	D.	Bacteria with the recombinant vector will be sensitive to antibiotic treatment and form white colonies in the presenceof X-gal.
	E.	None of these are correct.

Answer 1

The transformed bacterial cells will be resistant to antibiotic because the antibiotics resistant genes are present in the cloning vector.Hence when inserted in bacterial cells these genes provide resistance to antibiotics.

The colonies will be white if the cells are transformed the main reason being alpha complementation will not be able to be completed and hence b-galactosidases will not be synthesised and no cleavage of substrate X-gal will be possible so no colour formation.Hence colonies remain white.So correct answer is B.