In the above represented plasmid, an alien piece of DNA is inserted at EcoRI site. Which of the following strategies will be chosen to select the recombinant colonies?
- A
Blue color colonies grown on ampicillin plates can be selected.
- B
Using ampicillin & tetracycline containing medium plate.
- C
Blue color colonies will be selected.
- D
White color colonies will be selected.
The EcoRI site lies inside the -galactosidase gene. Inserting alien DNA here causes insertional inactivation of the gene, so recombinant cells can no longer produce the blue colour in the presence of the chromogenic substrate.
Therefore:
- Recombinant colonies → white
- Non-recombinant colonies → blue
Ampicillin and tetracycline resistance genes remain intact in both types, so they cannot by themselves distinguish recombinants.
Select white colonies.
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