THE MOLECULAR BASIS OF INHERITANCE
RECOMBINANT DNA
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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form white colony in X-gal
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form blue colony in X-gal
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form colorless colony in X-gal
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do not form any colony on X-gal
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Detailed explanation-1: -Plasmids used in cloning contain an antibiotic resistance gene. Thus, all of the bacteria are placed on an antibiotic plate to select for ones that took up a plasmid. Bacteria without a plasmid die.
Detailed explanation-2: -Bacteria without the plasmid are less likely to survive and reproduce. Some plasmids take extreme measures to ensure that they are retained within bacteria. For example, some carry a gene that makes a long-lived poison and a second gene that makes a short-lived antidote.
Detailed explanation-3: -For screening the clones containing recombinant DNA, a chromogenic substrate known as X-gal is added to the agar plate. If -galactosidase is produced, X-gal is hydrolyzed to form 5-bromo-4-chloro-indoxyl, which spontaneously dimerizes to produce an insoluble blue pigment called 5, 5’-dibromo-4, 4’-dichloro-indigo.
Detailed explanation-4: -Incorrect antibiotic If you plated on the correct antibiotic but still see few or no colonies, then you may need to re-check your ligation or assembly reaction. You may have used an incorrect part in your reaction, thus resulting in an incorrect antibiotic backbone.