A cloning vector has two antibiotic resistance genes- for tetracycline and ampicillin. A foreign DNA
was inserted into the tetracycline gene. Non-recombinants would survive on the medium containing :
1. ampicillin but not tetracycline
2. tetracycline but not ampicillin
3. both tetracycline and ampicillin
4. neither tetracycline nor ampicillin
(3) Both genes are functional in non-recombinants. In recombinants the gene for tetracycline resistance would be insertionally inactivated.