43. A student clones a gene of interest within the ampicillin resistance gene of pBR322 vector for
transformant selection, the student will use:
(a) Ampicillin plates ,
(b) Both Ampicillin plates and Tetracycline plates ,
(c) Neither Ampicillin plates nor Tetracycline plates ,
(d) Tetracycline plates

How to Select Recombinant Clones in pBR322 Vector: Understanding Antibiotic Resistance Markers

The pBR322 plasmid vector is a classic cloning tool that carries two antibiotic resistance genes: one for ampicillin (Amp^R) and another for tetracycline (Tet^R). These markers are crucial for screening recombinant bacteria.

When a gene of interest is inserted within the ampicillin resistance gene, the Amp^R gene is disrupted. This means:

• The bacteria lose resistance to ampicillin.

• The tetracycline resistance gene remains intact and functional.

What Does This Mean for Selection?

Let’s analyze the options based on this knowledge:

(a) Ampicillin plates

❌ Not ideal — Recombinant bacteria have disrupted Amp^R and will not grow on ampicillin.

(b) Both Ampicillin plates and Tetracycline plates

❌ Not necessary — Only one is sufficient to distinguish recombinants.

(c) Neither Ampicillin plates nor Tetracycline plates

❌ Incorrect — At least one antibiotic is needed to select for transformed cells.

(d) Tetracycline plates

✅ Correct Answer — Since the tetracycline resistance gene is not disrupted, transformed bacteria can grow on tetracycline, allowing successful selection.

Final Answer:

(d) Tetracycline plates

When cloning into the ampicillin resistance gene of pBR322, the recombinant bacteria lose Amp^R but retain Tet^R, so tetracycline plates are used for selection.