Selectable Markers

In this class we will discuss every minute details of role of Selectable Markers in recombinant DNA technology. Modern biotechnology is associated with recombinant DNA (rDNA) technology or genetic engineering involving the manipulation of desired genes. It enhances their productivity and also gives rise to new products. In the cloning vector pBR322, ampicillin and tetracycline resistance genes are the selectable markers. The role they play is that they help in the selection of transformed cells from non transformed cells. They also help distinguish recombinant cells from non-recombinant cells.The coding sequence of an enzyme β-galactosidase is preferred over antibiotic resistance genes because recombinants can be easily visualised and the process is comparatively simple and less cumbersome. When the foreign gene is inserted within the β-galactosidase gene, the enzyme p-galactosidase gets inactivated (insertional inactivation). Thus, when the bacteria are grown on a chromogenic substrate, non-recombinanats will produce blue-coloured colonies while the recombinants will produce colourless colonies.