Gene probes can be labeled by which methods?

• A. Radioactive labeling
• B. Fluorescent labeling
• C. No labeling needed
• D. Both radioactive and fluorescent labeling

Answer: (D)

Labeling gene probes makes them detectable after they hybridize to their target sequences. Probes can be marked with radioactive isotopes, such as 32P or 35S, and detected by autoradiography or phosphorimaging, which provides very high sensitivity for detecting even tiny amounts of target nucleic acid. At the same time, probes can be labeled with fluorescent dyes, which glow under specific light and are read with fluorescence scanners or microscopes. This non-radioactive approach is safer, allows easy multiplexing with different colors, and is convenient for many modern workflows. Some methods also use enzymatic or affinity labels (like biotin or digoxigenin) detected indirectly, but the common, widely used labeling strategies are radioactive and fluorescent. Since the signal is needed to visualize hybridization, labeling is essential rather than optional. Therefore, gene probes can be labeled by either radioactive or fluorescent labeling.