Identify the selectable markers $a,b$ in the diagram of $E.coil$ vector shown above.

Selectable markers are the genetic markers that select a particular host cell according to the markers present. These host cells have vectors and are resistant to the particular type of antibiotics. The plasmid has mostly two types of selectable markers:

1. Ampicillin
2. Tetracyclin

The plasmids are the cloning vectors that are resistant to the antibiotics ampicillin and tetracycline.

So, A is 'ampicillin' and B is tetracycline'.