What is used as a marker gene to show that the human gene has been taken up or expressed?

• A. Housekeeping gene
• B. Antibiotic resistance marker
• C. Lactose metabolism gene
• D. Cell wall synthesis gene

Answer: (B)

Marker genes act as flags to show which cells have taken up the introduced DNA. An antibiotic resistance marker is the standard choice because it lets you select for cells that received the construct: only those cells survive in the presence of the antibiotic, indicating uptake (and, if the marker is active, expression of the construct). Housekeeping genes are typically used as internal controls, not as markers for uptake or expression. Lactose metabolism or cell wall synthesis genes aren’t used as general markers for this purpose. So the antibiotic resistance marker best indicates that the human gene has been taken up (and possibly expressed).