What is the role of a marker gene in plasmids?

• A. To act as marker gene
• B. To increase transformation success
• C. To enhance nutrient uptake
• D. To produce color in colonies

Answer: (A)

Marker genes in plasmids provide a detectable signal that lets you know which cells actually took up the plasmid. They serve as a selectable indicator: by linking a trait such as antibiotic resistance (or a fluorescent protein) to the plasmid, only the cells that carry the plasmid will survive on selective media or glow under appropriate light. This makes it practical to distinguish transformed cells from those that didn’t take up the plasmid, which is the main purpose of having a marker gene. The marker isn’t inherently increasing the chance of transformation itself, and it isn’t about nutrient uptake. Some markers do produce color or fluorescence, but that visual cue is a consequence of the marker, not the underlying role of identifying successful transformants.