Which term best describes the color observed for DNA staining in this image?

• A. Red
• B. Blue
• C. Green
• D. Purple

Answer: (A)

DNA staining color in a fluorescence image corresponds to the emission color of the DNA-binding dye used. A red signal means the dye bound to the DNA emits red light when excited, so DNA-rich regions like nuclei appear red. This red-emitting dye could be propidium iodide or another red-fluorescent DNA stain, and the microscope is set to detect red fluorescence. If blue were seen, it would point to a blue-emitting DNA dye such as DAPI; green would indicate a green fluorophore like FITC; purple could arise from overlap of red and blue channels or a dye with a purple emission. So the observed red color best matches DNA staining with a red-emitting fluorophore.