What is the purpose of adding an antibiotic resistance gene into a DNA fragment before inserting it in a cell?

• A. It protects the transgene from destruction by bacteria.
• B. It helps identify the cells which have integrated the transgene.
• C. It protects the animal receiving the transgene from bacterial infection.
• D. It promotes cell division.

Answer: (B)

Antibiotic resistance genes act as selectable markers. When the DNA fragment containing the transgene is introduced into cells, including the resistance gene, you apply the antibiotic during culture. Only cells that have taken up and express the introduced DNA—and thus carry the resistance gene—survive in the antibiotic’s presence. This makes it possible to identify and isolate the cells that have integrated the transgene from those that didn’t. It isn’t about protecting the animal, promoting division, or shielding the transgene from destruction; it’s a screening tool to distinguish successful transfections.