(i) Desirable characters of an ideal cloning vector : 

• Origin of replication: It is a specific sequence of nucleotides which serves as binding site for initiator protein (Helicase) to start replication. Any foreign DNA linked with vector DNA also gets replicated along with it, hence is important for maintaining the copy number of foreign DNA.

• Selectable markers : Cloning vectors must contain atleast one selectable marker or it helps in: – detection of transformed host cells, – Identification and elimination of nontransformed post cells, – Isolation and growth of transformed host cells. 

• Cloning sites : A cloning site is a restriction endonuclease recognition site or target site in vector DNA. It has palindromic sequence of nitrogenous bases cut by a specific restriction endonuclease enzyme for insertion and linking of foreign DNA. 

• Small size: A vector should be small in size because large molecules bind is break up during isolation and purification.

(ii) Two vectorless methods of gene transfer used in rDNA technology. 

• Chemical mediated gene transfer: Use of chemicals like polyethene glycol (PEG) and dextron sulphate induces DNA uptake by plant protoplast 

• Electroporation : Short electric impulse of high voltage causes fine transient forces in cell membrane through which foreign DNA enters into the cell.