The document discusses different types of probes used in animal cell biotechnology and genetics. A probe is a labelled DNA or RNA molecule that is single stranded and used to search for a sequence of interest from a mixture of nucleic acids. There are three main types of probes: enzymatic probes which detect target proteins using enzymes, fluorescence probes which use fluorescent molecules to detect target molecules, and radioactive probes which use a radioisotope to label nucleic acid fragments of interest. Enzymatic probes work by conjugating an enzyme to another protein like biotin, which binds to the target molecule, and adding a substrate that produces a visible reaction.