→ In addition to 'ori', the vector requires a selectable marker.
→ It helps in identifying and eliminating non transformants and selectively permitting the growth of the transformants.
→ Transformation is a procedure through which a piece of DNA is introduced in a host bacterium,
→ Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli.
→ The normal E. coli cells do not carry resistance against any of these antibiotics.