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A foreign DNA fragment is successfully ligated into the pBR322 cloning vector at the Sal I restriction site. The resulting recombinant plasmids are then transformed into host E. coli cells. What will be the growth characteristics of these recombinant E. coli cells when plated on media containing different antibiotics?

Options

  1. AThey will grow on tetracycline-containing medium but fail to grow on ampicillin-containing medium.
  2. BThey will grow on ampicillin-containing medium but fail to grow on tetracycline-containing medium.
  3. CThey will grow on both ampicillin and tetracycline-containing media.
  4. DThey will fail to grow on both ampicillin and tetracycline-containing media.

Correct answer

B. They will grow on ampicillin-containing medium but fail to grow on tetracycline-containing medium.

Step-by-step solution

In the pBR322 cloning vector, the restriction site for the enzyme Sal I is located within the tetracycline resistance ( tet^R ) gene. When a foreign DNA fragment is ligated at the Sal I site, it causes insertional inactivation of the tet^R gene. As a result, the recombinant plasmid loses its resistance to tetracycline. However, the ampicillin resistance ( amp^R ) gene remains intact and functional. Therefore, the recombinant E. coli cells will be able to grow on an ampicillin-containing medium but will fail to grow

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