Pathology dictionary

Fluorescence in situ hybridization

What is fluorescence in situ hybridization?

Fluorescence in situ hybridization (FISH) is a molecular test pathologists perform to learn more about the genetic material in a cell. FISH is commonly used to look for genetic changes in tumours.

Normal DNA

Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce piece of the machine called a protein. Most DNA is stored in a part of the cell called the nucleus.

How does fluorescence in situ hybridization work?

Fluorescence in situ hybridization uses a fluorescent probe which has been designed to stick to a unique segment of DNA (the target). FISH probes are called fluorescent because they only produce a colour when they are exposed to certain types of light. As a result, pathologists need to use a special type of microscope which can produce specific types of light and detect the colour coming from the probe.

The results are captured in an image on a computer for further analysis. When the probe finds a change in the location of the target DNA, the result is called a translocation. When the probe finds a change in the total amount of target DNA, the result is called an amplification or deletion depending on the type of change identified.​

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