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In a cloning experiment, a recombinant DNA is inserted within the coding sequence of the enzyme -galactosidase in a plasmid vector. This vector also carries an ampicillin resistance gene. The bacterial cells after transformation are plated on an agar medium containing ampicillin and a chromogenic substrate. It is observed that some colonies are blue while others are white. Which of the following cells are responsible

Options

  1. ATransformed cells containing the non-recombinant vector
  2. BNon-transformed cells
  3. CTransformed cells containing the recombinant vector
  4. DTransformed cells in which the ampicillin resistance gene is insertionally inactivated

Correct answer

C. Transformed cells containing the recombinant vector

Step-by-step solution

The plating medium contains ampicillin, which acts as a selectable marker to eliminate non-transformed cells. Only transformed cells (containing either recombinant or non-recombinant vectors) will grow and form colonies. The chromogenic substrate is used to screen for recombinants. In non-recombinant vectors, the -galactosidase gene is intact, so the cells produce the enzyme which cleaves the chromogenic substrate to form blue colonies. In recombinant vectors, the insertion of alien DNA within the coding sequence o

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