Fluorescence in situ hybridization (FISH) is a test that maps the genetic make up in a person’s cells. This test can be used to analyze specific genes or portions of genes. It is mainly used for detection of cancer cells and detect gene or chromosome abnormalities.
FISH is a very inherent part of cytogenetics used to study DNA or RNA sequences in specific regions of the chromosomes using fluorescent probes which duplicate the primary sequences. FISH helps to detect any kind of chromosomal abnormalities or dislocations caused due to any disease or chemical imbalance in the body. Cancer patients and unborn babies are the primary beneficiaries of FISH (FLuorescence in Situ Hybridization).
DNA is a double stranded molecule, and when it is chemically denatured and separated into two strands, it quickly rearranges into a double stranded conformation. Thus, when a single stranded probe is incubated with a single-stranded (denatured) metaphase chromosome (or interphase), the probe will bind to complementary DNA sequences to reform the double stranded molecule. Overall, the most critical step when using FISH is the choice of adequate probes. A DNA probe is defined according to its target or complementary DNA in metaphase and interphase cells: (1) repetitive sequence probe, (2) whole chromosome (painting), (3) locus-specific probes.
FISH is widely used for several diagnostic applications: identification of numerical and structural abnormalities, characterization of marker chromosomes, monitoring the effects of therapy, detection of minimal residual disease, tracking the origin of cells after bone marrow transplantation, identification of regions of deletion or amplification, detection of chromosome abnormalities in non-dividing or terminally differentiated cells, determination of lineage involvement of clonal cells…
Moreover it has many applications in research: identification of non-random chromosome rearrangements, identification of trans-location molecular breakpoint, identification of commonly deleted regions, gene mapping, characterization of somatic cells hybrids, identification of amplified genes, study the mechanism of rearrangements. FISH is also used to compare and study two biological species to trace evolutionary relationships.
There are mainly two types of probes used in FISH.
Locus specific probes hybridize to a particular region of a chromosome. This type of probe is useful when scientists have isolated a small portion of a gene and want to determine which chromosome that gene is located on. They prepare a probe from the piece of the gene and observe which chromosome the probe hybridizes to.
Alphoid or centromeric repeat probes are generated from repetitive sequences found at the centromeres of chromosomes. Because each chromosome is painted in a different color, researchers use this technique to determine whether an individual has the correct number of chromosomes.
FISH (Fluorescent in situ Hybridization) is a very versatile method that can br used for prenatal,post natal, cance and preimplantation genetic testing with minimal expenses and patient care services included.
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