Selectable markers show the success of a transfection or other procedure meant to introduce foreign DNA into a cell . They are a type of reporter gene used in laboratory microbiology , molecular biology , and genetic engineering to indicate the success of a transfection or other procedure meant to introduce foreign DNA into a cell . Selectable markers are often antibiotic resistance genes ; bacteria that have been subjected to a procedure to introduce foreign DNA are grown on a medium containing an antibiotic , and those bacterial colonies that can grow have successfully taken up and expressed the introduced genetic material .