The fundamental process of FISH involves several steps: 1. Sample Preparation: Biological samples, such as tissue sections or cells, are fixed onto a slide. 2. Probe Labeling: Single-stranded DNA or RNA probes are labeled with fluorescent dyes. 3. Hybridization: The labeled probes are applied to the sample, where they hybridize to their complementary sequences. 4. Washing: Excess probes are washed away to reduce background noise. 5. Detection: The sample is examined under a fluorescence microscope to visualize the hybridized probes.