fluorescent in situ hybridization

(flə¦res·ənt in¦sit′chü ′hī·brə·də′zā·shən)

(genetics) A technique in which a deoxyribonucleic acid (DNA) probe is labeled with a fluorescent dye (that can be visualized under a fluorescent microscope) and then hybridized with target DNA, usually chromosome preparations on a microscopic slide. It is used to precisely map genes to a specific region of a chromosome in prepared karyotype, or can enumerate chromosomes, or can detect chromosomal deletions, translocations, or gene amplifications in cancer cells. Abbreviated FISH.

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FISH (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 probe of specific 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. Hybridized regions of the chromosome fluoresce. This is a type of karyotypic analysis that can generate a physical map matching clones and gene markers to specific parts of a chromosome.

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