NEETZoologyBiotechnology - Principles and Processes
A researcher ligates a foreign DNA fragment into the Sal I restriction site of the standard pBR322 vector. The resulting plasmid mixture is transformed into host E. coli cells. The cells are first plated on a medium containing ampicillin, and then the growing colonies are replica-plated onto a medium containing tetracycline. What will be the growth pattern of the recombinant colonies on these two antibiotic plates?
Options
- AThey will grow on the ampicillin plate but not on the tetracycline plate.
- BThey will grow on both the ampicillin and tetracycline plates.
- CThey will grow on the tetracycline plate but not on the ampicillin plate.
- DThey will not grow on either of the antibiotic plates.
Correct answer
A. They will grow on the ampicillin plate but not on the tetracycline plate.
Step-by-step solution
In the pBR322 vector, the Sal I restriction site is located within the tetracycline resistance gene. Insertion of a foreign DNA fragment at this site causes insertional inactivation of the tetracycline resistance gene, making the recombinant plasmids sensitive to tetracycline. The ampicillin resistance gene remains intact. Therefore, the recombinant E. coli colonies will be resistant to ampicillin but sensitive to tetracycline. They will grow on the ampicillin-containing medium but will fail to grow when replica-pl