CBSE Class 12-science Answered

(i) A cloning vector must possess the following characteristics:

(a) Relaxed origin of replication (ori)

(b) Selectable marker, genes encoding for an antibiotic resistance or genes encoding for -galactosidase to identify and eliminate non-transformants.

(c) Cloning site or recognition site for the restriction enzyme to recognise.

(ii) DNA is a hydrophilic molecule. Therefore, it cannot pass through the cell membrane. The bacterial cells can be made competent by treating them with a specific concentration of a divalent ion like calcium. The cells are then incubated on ice followed by a heat shock treatment by placing them briefly at 42C and then putting back on ice.