Biology · Principles and Processes in Biotechnology

In recombinant DNA technology, the selection of recombinants based on insertional inactivation of the beta-galactosidase coding gene produces white colonies because:

1. Recombinant plasmids produce an altered enzyme that bleaches the chromogenic substrate.
2. Insertional inactivation prevents the synthesis of beta-galactosidase, producing no colour.
3. Beta-galactosidase catalyzes the degradation of the chromogenic substrate to a colourless gas.
4. Host cells lack the transport system for chromogenic substrate uptake.