Fluorescence in situ hybridization: An important molecular cytogenetic method for identifying chromosomes and parts of chromosomes, deciphering chromosome rearrangements, and locating genes on chromosomes.
"Fluorescence" means emitting light that comes from a reaction within the emitter. "In situ" refers to the fact that this techniques is done with the chromosomes, cells or tissue in place (in situ) on a microscope slide.
In situ hybridization is a technique in which single-stranded nucleic acids (DNA or RNA) are permitted to interact so that complexes, or hybrids, are formed by molecules with sufficiently similar, complementary sequences. Through nucleic acid hybridization, the degree of sequence identity can be determined and specific sequences detected and sometimes those sequences can be located on a specific chromosome. A nucleic acid labelled with a fluorescent dye is hybridized to suitably prepared cells or histological sections. This is used particularly to look for specific transcription or localization of genes to specific chromosomes.
Fluorescence in situ hybridization is abbreviated FISH.