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in Biology by (61.9k points)

(a) Name the selectable markers in the cloning vector pBR322. Mention the role they play.

(b) Why ls the coding sequence of an enzyme β- galactosidase a preferred selectable marker in comparison to the ones named above ?

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(a) ampR / ampicillin resistance genes, tetR/ tetracycline resistance gene.

They help in identifying and eliminating non -transformants/non recombinants and selectively permitting the growth of the transformants / recombinants.

(b) Simpler process / less cumbersome, in the presence of chromogenic substrate recombinants are colourless and non recombinants are blue in colour. 

Detailed Answer:

(a) In cloning vector pBR322, ampicillin and tetracycline resistance genes serve as selectable markers. Selectable markers help in the identification and selection of transformed cells from non-transformed cells to distinguish the recombinant cells from the non-recombinant cells. 

(b) The coding sequence of an enzyme β-galactosidase is preferred over antibiotic resistance genes because recombinants can be easily visualised and the process is comparatively simple and less cumbersome. When the foreign gene is inserted within the β-galactosidase gene, the enzyme p-galactosidase gets inactivated (insertional inactivation). Thus, when the bacteria are grown on a chromogenic substrate, non-recombinanats will produce blue-coloured colonies while the recombinants will produce colourless colonies.

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