In genetic engineering, the antibiotics are used for?

Explanation

Selectable markers are those genes which help in selecting those host cells which contain vectors (i.e., transformants) and eliminating the non­transformants. The genes encoding resistance to antibiotics such as tetracycline, ampicillin, kanamycin etc., are useful selectable markers. E.coli. Plasmid pBR322 has two resistance genes - ampicillin resistance (amp r) and tetracycline resistance (tet r) which are considered useful for selectable markers. The presence of restriction sites within the markers tet r and amp r permits an easy selection for cells transformed with the recombinant pBR322. Insertion of the DNA fragment into the plasmid using enzyme Pst I or Pvu I places the DNA insert within the gene amp r; this makes amp r nonfunctional. Bacterial cells containing such a recombinant pBR322 will be unable to grow in the presence of ampicillin but will grow on tetracycline. Similarly, when the restriction enzyme Bam HI or Sal I is used, the DNA insert is placed within the gene tet r making it nonfunctional. Bacterial cells possessing such a recombinant pBR322 will, therefore, grow on ampicillin but not on tetracyclin.