During a genetic engineering experiment, a bacterial culture is transformed with a plasmid vector containing an ampicillin resistance gene and a functional -galactosidase gene. The cells are then plated on an agar medium containing ampicillin and a chromogenic substrate. A student observes several well-isolated blue colonies growing on the plate. What is the exact genetic nature of the cells forming these blue coloni

Step-by-step solution

The cells are able to grow and form colonies on an ampicillin-containing medium, which indicates that they have successfully taken up the plasmid. Therefore, they are transformants. The colonies are blue in colour in the presence of a chromogenic substrate, which means the -galactosidase gene is intact and functional. If a foreign DNA had been inserted into this gene, it would have undergone insertional inactivation, resulting in white colonies. Since the gene is intact, the plasmids inside these cells do not carry