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	Identification It's now time to select the cells that contained the wanted recombinant plasmid. Separation of cells that have pick up the plasmids. The bacteria will be plated onto nutrient agar plates which contain the antibiotic ampicillin, resistance to which is encoded by pBR322. Since E. coli is killed by ampicillin, cells which can grow in the nutrient agar containing ampicillin must have pick up the plasmid and thus the ampicillin-resistance gene. These cells however could have picked up the non-recombinant plasmid and not the recombinant plasmid. So to distinguish the two:
	Replica plate the cells obtained onto nutrient agar containing tetracycline.  Reason is that the target DNA is inserted into the tetracycline-resistance conferring gene in pBR322. This will inactivate the gene conferring resistance to tetracycline. Cells which carry non-recombinant DNA are resistant to both tetracycline and ampicillin. But cells which carry the recombinant DNA will be resistance only to ampicillin but susceptible to tetracycline.     By referring to the master plate, those colonies that disappear in tetracycline are the E. coli cells that contain the final recombinant DNA.
	By referring to the master plate, those colonies that disappear in tetracycline are the E. coli cells that contain the final recombinant DNA.
	Relating Topics - Vectors - Overview of the Structure of DNA