In vector pBR322, it has two restriction site BamHI and Pst I, which are responsible for tetracycline and ampicillin antibiotic resistance respectively. Ligation of alien DNA at BamHI in vector, inactivate tetracycline antibiotic resistance gene but ampicillin resistance gene still actual. When we grow that vector in tetracycline medium, the cell will no longer survive due to the absence of tetracycline resistance gene.