Chromosomal Banding

Fluorescence in situ hybridization (FISH) is a molecular cytogenetic technique that allows cytogeneticists to analyze chromosome resolution at the DNA or gene level. FISH can be performed on dividing (metaphase) and non-dividing (interphase) cells to identify numerical and structural abnormalities resulting from genetic disorders.

In FISH, cytogeneticists utilize one or more FISH probes that typically fall into one of the following three categories:

1. Repetitive sequences, including alpha satellite DNA, that bind to the centromere of a chromosome;
2. DNA segments, representative of the entire chromosome, that will bind to and cover the entire length of a particular chromosome; and
3. DNA segments from specific genes or regions on a chromosome that have been previously mapped or identified.

A probe is "tagged" either directly, by incorporating fluorescent nucleotides, or indirectly, by incorporating nucleotides with attached small molecules, such as biotin, digoxygenin, or dinitrophenyl, to which fluorescent antibodies can later be bound. The probe and the chromosomes (from either the metaphase or interphase cells) that are being analyzed are denatured and allowed to bind or hybridize to one another. If necessary, antibodies with a fluorescent tag are applied to the cells. The cells are then viewed with a fluorescence microscope. The fluorescent signals represent the probe(s) that is bound to the chromosomes.