The ampicillin resistance gene

• In order to find out which bacterial cells have taken up the plasmid, a specific gene for antibiotic resistance is used. This gene should be unaffected by the introduction of a new gene, such as the ampicillin resistance gene.
• To identify which bacterial cells have taken up the plasmids (using the ampicillin resistance gene), firstly the bacteria should be grown on a medium containing the antibiotic ampicillin. The bacteria that have taken up the plasmids will possess ampicillin resistance, and are therefore able to break down ampicillin and survive.
• The bacterial cells that have not taken up the plasmids will not possess the ampicillin resistance gene, and will therefore die in the presence of ampicillin.
• Using the ampicillin resistance gene is an effective method of showing which bacterial cells have taken up the plasmids. However, some cells will have taken up the plasmids which closed up without incorporating the gene, and these cells will have also survived.