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Question

The colonies of recombinant bacteria appear white in contrast to blue colonies of non-recombinant bacteria because of

A
Inactivation of glycosidase enzyme in recombinant bacteria
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B
Non-recombinant bacteria containing beta galactosidase
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C
Insertional inactivation of alpha galactosidase in non-recombinant bacteria
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D
Insertional inactivation of alpha galactosidase in recombinant bacteria
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Solution

The correct option is B Non-recombinant bacteria containing beta galactosidase
Alternative selectable markers
Alternative selectable markers differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate.

Insertional inactivation
Insertional inactivation is the process of inactivation of a marker gene by the insertion of foreign gene in its coding sequence. For example, insertion of a foreign gene in the coding sequence of 𝛽-galactosidase gene.

Insertional inactivation in β galactosidase gene
  • Insertional inactivation in β galactosidase gene is as follows:
  • Insertion of a foreign gene in the coding sequence of β galactosidase gene, synthesize a non-functional enzyme. It does not convert chromogenic substrate into a product.
  • Hence only the non-recombinant colonies produce blue colour due to the presence of chromogenic substrate and absence of insert.
  • The recombinants will produce white colonies in the presence of chromogenic substrate.
  • This makes it easy to identify recombinants and non-recombinants.
Final answer:
c. Non-recombinant bacteria containing beta galactosidase

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