FISH (an acronym that stands for fluorescent in situ hybridization) is a method in which a clone gene is “painted” with a fluorescent dye and mapped to a chromosome. In FISH, cells are arrested in the metaphase stage of mitosis and placed on a slide where they burst open, spreading chromosomes over the surface. A fluorescent-labeled DNA “piece” of interest is placed on the slide and incubated long enough for hybridization to occur. The slide is then viewed under a fluorescence microscope that focuses ultraviolet light on the chromosomes, and the researcher will view hybridized regions of the chromosome that fluoresce. This can generate a physical map matching clones and gene markers to specific parts of a chromosome.