fluorescence in situ hybridization (floor-EH-sents in SY-too HY-brih-dih-ZAY-shun)
A laboratory method used to look at genes or chromosomes in cells and tissues. Pieces of DNA that contain a fluorescent dye are made in the laboratory and added to a cell or tissue sample. When these pieces of DNA bind to certain genes or areas on chromosomes in the sample, they light up when viewed under a microscope with a special light. FISH can be used to identify where a specific gene is located on a chromosome, how many copies of the gene are present, and any chromosomal abnormalities. It is used to help diagnose diseases, such as cancer, and help plan treatment. Also called FISH.