NEET2026BiologyChapterActual
During a cloning experiment, a foreign DNA fragment is ligated into the cloning vector pBR322 at the Pst I restriction site. If these recombinant plasmids are successfully transformed into host E. coli cells, which of the following correctly describes the growth characteristics of the recombinant transformants?
Options
- AThey will be able to grow on an agar plate containing both ampicillin and tetracycline.
- BThey will be able to grow on a tetracycline-containing medium but not on an ampicillin-containing medium.
- CThey will be able to grow on an ampicillin-containing medium but not on a tetracycline-containing medium.
- DThey will be sensitive to both ampicillin and tetracycline, failing to grow on either medium.
Correct answer
B. They will be able to grow on a tetracycline-containing medium but not on an ampicillin-containing medium.
Step-by-step solution
The cloning vector pBR322 contains two antibiotic resistance genes: ampicillin resistance ( amp^ R ) and tetracycline resistance ( tet^ R ). The restriction site for the enzyme PstI is located within the ampicillin resistance gene ( amp^ R ). When a foreign DNA fragment is ligated at the PstI site, it leads to the insertional inactivation of the amp^ R gene. As a result, the recombinant plasmid loses its resistance to ampicillin. Since the tetracycline resistance gene ( tet^ R ) remains intact, the recombinant tran