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Biochemistry · Topic

FISH (fluorescence in situ hybridization) !

FISH uses fluorescent DNA probes that stick to one exact place on a chromosome, to see under the microscope whether a piece is missing, extra or moved.

Updated 2026-11-01

Key facts

  • A fluorochrome-labelled DNA probe hybridises to its complementary sequence in fixed chromosomes or nuclei.
  • It detects microdeletions, duplications, aneuploidies and translocations too small for a standard karyotype.
  • It works on interphase nuclei: no dividing cells are needed, so results are fast.
  • Examples: 22q11.2 microdeletion (DiGeorge), t(9;22) BCR-ABL (chronic myeloid leukaemia), HER2 amplification in breast cancer.

In detail

  • Steps: fix cells or tissue → denature the DNA → apply the probe → hybridise → wash → view under a fluorescence microscope.
  • Probe types: locus-specific (one gene), centromeric (count chromosomes), whole-chromosome paint, and fusion or break-apart probes (translocations).
  • A missing signal means deletion; extra signals, duplication or aneuploidy; two colours together, a gene fusion.
  • Chromosomal microarray (CMA) now finds many microdeletions at once; FISH is still useful for confirmation and for tumour tissue.
Also called
Fluorescence in situ hybridisation

Clinical notes

  • HER2 amplification by FISH in breast cancer points to anti-HER2 targeted therapy.
  • Rapid prenatal FISH counts chromosomes 13, 18, 21, X and Y in amniotic fluid.

Test yourself

Think of the answer, then tap the question to see it.

What advantage does FISH have over a standard karyotype?

It finds submicroscopic changes (microdeletions) and works on interphase nuclei, without culturing dividing cells.

Which FISH finding suggests a microdeletion?

The probe signal is missing on one of the two homologous chromosomes.

What is FISH used for in breast cancer?

To measure HER2 gene amplification and decide whether anti-HER2 therapy fits.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Fluorescence In Situ Hybridization Fact Sheet (National Human Genome Research Institute (NHGRI), 2026); Fluorescence In Situ Hybridization (FISH) (National Human Genome Research Institute (NHGRI), 2026); What are the different types of genetic tests?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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