Question

How does the Ampicillin resistance “selectable marker” allow you to tell the difference between transformed and untransformed bacteria in this experiment?

Answer 1

Transformation is a process where forgeign DNA is taken by a cell. In a laboratory, plasmids with the desired gene insert are transformed into the bacterial cell and expressed using bacterial expression system. In order to identify whether bacteria has taken up the plasmid, selectable markers are used. One most commonly used such marker is antibiotic resistance genes. In this case, ampicillin resistance is used as a selectable marker. That means plasmid contains ampicillin resistance genes. Once transformation process is done, bacteria are grown in the media containing ampicillin antibiotic. Bacteria which have taken up the plasmid (transformed bacteria) have expressed ampicillin resistance machinery. Hence show resistance towards ampicillin and grow in the presence of ampicillin whereas those bacteria which have not taken up the plasmid ( non-transformed bacteria) get killed in the media containing ampicillin. Thus ampicillin resistance acts as a selectable marker to identify the transformed cells from the untransformed cells.