Fluorescence In Situ Hybridization (FISH)

Fluorescence in situ Hybridization
Fluorescence in situ hybridization (FISH) allows for the identification of cryptic or complex chromosomal abnormalities. Red/Green Cytocell© Williams-Beuren Syndrome Region Probe. Aqua PAX5 gene on 9p13.

Fluorescence in situ hybridization (FISH) detects the presence/absence or location of a specific gene or chromosome at ~ 100kb resolution. FISH studies are useful to demonstrate micro deletions or duplications and to demonstrate the presence of gene rearrangements. FISH also permits rapid detection of monosomies, trisomies, and numerical sex chromosome abnormalities.


  • To confirm patient/sample-specific gene or chromosome abnormality when the target is known
  • To identify microdeletions and duplications when the target is known
  • For faster mosaicism screening if a specific chromosome aneuploidy is suspected
  • Transgene mapping


FISH involves the hybridization of a target DNA sequence labeled with a fluorescent dye (called a probe). Probes are currently available from a number of vendors or can be produced in our laboratory. Probes can be specific to unique sequences (e.g., ELN gene for Williams Syndrome on chromosome 7), or repetitive DNA (e.g., alpha-satellite centromere sequences), or chromosome paints (e.g., sequences that comprise chromosome 7). FISH analysis can be performed using one or multiple probes, provided the fluorescent labels for each probe are different and the microscope has the appropriate filter to detect the label. FISH can be performed on harvested metaphase cells, interphase cells, or on direct cell preparations. A FISH analysis includes examination of 20 metaphase cells or 100 interphase cells. Color fluorescence photomicrographs of representative FISH findings are provided.

For further information regarding how FISH is used to detect chromosome abnormalities, please visit FISHing for Chromosomal Abnormalities.