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Kingdom Monera

Bacterial col...

Question

Bacterial colonies that have a foreign DNA fragment inserted in to the plasmid will appear white because:

A

X-gal can be cleaved by

β

- galactoxidase

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B

Gal gene shows insertional inactivation due to insertion of foreign DNA

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C

Gal gene is active

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D

X-gal can be cleaved by permease

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Solution

The correct option is D Gal gene shows insertional inactivation due to insertion of foreign DNA
The blue-white screening test helps to differentiate the recombinant plasmid from a non-recombinant plasmid. The bacterial cell that is transformed with a vector containing recombinant DNA will produce white colonies whereas bacterial cell that is transformed with the vector without recombinant DNA will produce blue colonies. In this, foreign DNA is inserted to interrupt the beta-galactosidase coding sequence, which otherwise reacts with x-gal substrate to produce a blue color. Due to the defective enzyme produced by insertion of foreign DNA in gal gene, white colored colonies are produced.
Thus, the correct answer is option B.

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