The extent of digestion of genomic DNA of donor organism is tested with the help of the following technique.

The isolated genomic DNA is subjected to incubation in a restriction endonuclease to cut the DNA into fragments of variable lengths. The extent of digestion is tested by gel electrophoresis during which if DNA bands of gel are formed almost towards the anode, one can understand the digestion is complete. If DNA bands are seen only nearer to cathode, one can understand the digestion is incomplete.