The introduction of fluorescent dyes into molecular biology techniques in the 1980s greatly improved techniques for visualizing DNA probes, and has allowed for the development of methods to visualize specific DNA sequences on human chromosomes using the microscope. The term "fluorescent in situ hybridization" (FISH) was adopted as a descriptive name for this methodology which combines techniques of molecular biology and cytogenetics (the study of chromosomes).

Using this technique, DNA probes are labeled with fluorescent dyes and hybridized to metaphase chromosome spreads on glass slides. DNA stains are used to visualize the unlabeled portions of the chromosomes. Thus, this method has become a means of identifying specific DNA sequences on metaphase chromosomes.

Initially, only single-color detection was possible, which limited most applications to the study of a single gene or region of the chromosome. The development of more sophisticated fluorescence filters and a variety of different...