Dear student,
In case of autoradiography, probe sequences are determined by application of radiolabeled ligands in the sections in inspection. Usually ligands are marked with 3H or 125I isotopes are used, although in cases of RNA or DNA viral sequences, 32P, 33P or 35S probes are also useed. Via marking and detecting the radioactive emissions from the probes attached, the sequence patterns and the functional patterns are detected.
Regards.