Antibiotic resistance gene present in vector acts a selectable marker. Selectable marker identifies transformant from non- transformants. The genes encoding resistance to antibiotic such as ampicillin, chloramphenicol, tetracycline are serve as selectable markers.
Addition of selectable marker or antibiotic resistance allows the host organism to survive. Generally, ampicillin, tetracycline etc are the useful selectable marker in E. coli.
