Fluorescent in situ hybridization (FISH) is a technique that uses a short strand of DNA tagged with a fluorescent dye to detect genetic abnormalities, including chromosomal deletions, rearrangements, or translocations, and to visualize specific genes. FISH is commonly used in cancer diagnosis and treatment, but it cannot be used as a general screening tool and may not be available in all laboratories or hospitals.
Fluorescent in situ hybridization, also known as fluorescent in situ hybridization, is more commonly referred to as FISH. It is a technique that involves using a short strand of DNA tagged with a fluorescent dye to detect genetic abnormalities. FISH allows researchers to visualize specific chromosomes, parts of chromosomes, or genes quickly and accurately. This is often used to determine the prognosis and treatment of certain diseases, especially cancers.
FISH is used to determine if chromosomes have abnormalities. This can include chromosomal deletions, rearrangements, or translocations, where two chromosomes have swapped segments. FISH also allows researchers to visualize specific genes. It can determine if a certain gene is present, where it is located on the chromosomes, and if multiple copies are present. This is called gene mapping.
A person’s genetic makeup is contained in their DNA, which is found in the nuclei of all of their cells. DNA has two strands which are complementary to each other. In other words, they have molecules called base pairs that match each other exactly. Genes are segments of DNA that have a particular sequence of base pairs and are found on specific areas of chromosomes. Genes are inherited and determine how cells function, but they can also undergo mutations if the sequence of base pairs in DNA changes.
The fluorescent in situ hybridization technique takes advantage of the complementary nature of the DNA strands. The investigators create a probe first. This is a short, single strand of DNA that is complementary to the genetic sequence the investigator is looking for. The probe is then labeled or fixed to a fluorescent dye.
Cells from diseased tissue, such as a tumor biopsy, usually constitute the sample to be examined by FISH. The sample is heated to denature the DNA in the cell nuclei. This means that the double strands of DNA in the sample cells break to form single strands. A specific FISH probe is then hybridized with the sample. In other words, the single strand of the probe is introduced and fuses with the complementary single strand in the denatured sample cells.
Using a special fluorescence microscope, the researcher examines the sample. If the specific gene or chromosome is present in the sample cells, it will appear as a fluorescent light on a darker background. Researchers can easily see whether or not the gene is present and, if so, how many copies of the gene are present in each cell. If the researcher is looking for the location of a gene, they can see where it is on the chromosome. A normal light microscope cannot be used with FISH, because the fluorescent dye emits a very low level of light.
The use of DNA hybridization with probes was first realized in the 1960s; however, the probes were labeled with radioactive rather than fluorescent substances. This had several problems. Radioactive substances are inherently unstable, dangerous and require special protocols for disposal. It also takes a long time to measure the radioactive signal emitted by the hybrid probe. The fluorescent in situ hybridization technique overcomes most of these hurdles.
If investigators know which gene they are looking for, FISH is fast and accurate in finding it. FISH can be performed even if the cells are not actively dividing and provides more specific information about abnormalities in the chromosomes. More conventional techniques, such as carotyping, simply tell investigators the number and size of chromosomes within a cell.
Fluorescent in situ hybridization has disadvantages. Because the key to FISH is knowing the base pair sequence and/or location of a gene, it cannot be used as a general screening tool. It is also more expensive than other less specific techniques and may not be available in all laboratories or hospitals.
The advantages and disadvantages of Fluorescent In Situ Hybridization are best described by example. FISH is routinely used in breast cancer diagnosis to determine if a patient has multiple copies of a gene called HER2. This usually indicates a more aggressive form of breast cancer and that the patient should receive certain medications as part of their treatment. FISH can be used for this because the base pair sequence and chromosomal location of the HER2 gene are known. Conversely, FISH cannot be used to determine which unknown gene or genes caused breast cancer or for breast cancer screening in general.
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