[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › FISH (fluorescence in situ hybridization)

[Biochemistry](https://durgical.com/en/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.

## Related conditions

- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)

## Related

- [DNA microarrays](https://durgical.com/en/biochemistry/topics/dna-microarrays/)
- [DNA structure and chromatin](https://durgical.com/en/biochemistry/topics/dna-structure-and-chromatin/)
- [Southern, Northern and Western blots](https://durgical.com/en/biochemistry/topics/southern-northern-and-western-blots/)

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/fish/)

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

Sources: [Fluorescence In Situ Hybridization Fact Sheet](https://www.genome.gov/about-genomics/fact-sheets/Fluorescence-In-Situ-Hybridization) (National Human Genome Research Institute (NHGRI), 2026); [Fluorescence In Situ Hybridization (FISH)](https://www.genome.gov/genetics-glossary/Fluorescence-In-Situ-Hybridization-FISH) (National Human Genome Research Institute (NHGRI), 2026); [What are the different types of genetic tests?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/testing/types/) (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).

[← All of biochemistry](https://durgical.com/en/biochemistry/)

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/biochemistry/topics/fish/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/fish/