(1) As selectable markers
(2) To keep medium bacteria-free
(3) to detect alien DNA
(4) To impart disease-resistance to the host plant
Ans: (2) To keep medium bacteria-free
Sol. The correct answer is option (2) because antibiotics are used in RDT to keep medium or culture bacteria-free.
Selectable marker helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. They undergo insertional inactivation upon addition of alien DNA in their ORF.