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

A gene, whose expression helps to identify transformed cells is known as

1. selectable marker                 

2. vector

3. plasmid                                 

4. structural gene

How are transformants selected from nontransformants?

Why is a marker gene useful?

Selectable marker helps