Mention the role of selectable marker genes in genetic engineering.

Selectable marker genes are present in plasmids and they help in the selection of the transformants i.e the cells in which the plasmid is present from the non-transformants (those in which the plasmid is absent). These selectable marker genes may provide resistance to antibiotics such as the ampicillin resistant and the tetracycline resistant sites seen in the plasmid pBR322.If cells are transformed with this plasmid, then the cells can be selected by either growing them in a medium containing ampicillin or tetracycline. Only the cells that have the plasmid (transformed cells) will have resistance for the antibiotic and will be able to grow in the medium. The cells that are not transformed will not be able to grow in such a medium.