Simplify the following text for a Grade 14 native English-speaking person.
Original: 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 .
Simplified: 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 .