NHGRI logo

​Fluorescence In Situ Hybridization (FISH)

updated: May 20, 2022


Fluorescence in situ hybridization (abbreviated FISH) is a laboratory technique used to detect and locate a specific DNA sequence on a chromosome. In this technique, the full set of chromosomes from an individual is affixed to a glass slide and then exposed to a “probe”—a small piece of purified DNA tagged with a fluorescent dye. The fluorescently labeled probe finds and then binds to its matching sequence within the set of chromosomes. With the use of a special microscope, the chromosome and sub-chromosomal location where the fluorescent probe bound can be seen.



One method for localizing a piece of DNA within a genome is called fluorescence in situ hybridization, abbreviated FISH. In this approach, a fluorescent dye is attached to a purified piece of DNA, and then that DNA is incubated with the full set of chromosomes from the originating genome, which have been attached to a glass microscope slide. The fluorescently labeled DNA finds its matching segment on one of the chromosomes, where it sticks. By looking at the chromosomes under a microscope, a researcher can find the region where the DNA is bound because of the fluorescent dye attached to it. This information thus reveals the location of that piece of DNA in the starting genome.