Fluorescence in situ hybridization (FISH) is a molecular diagnostic technique that allows visualization of defined chromosomal nucleic acid sequences in a cell preparation. annealing the fluorescently labeled DNA probe to complementary targeted sequences. Thus, genes/sequences of interest could be observed visually using a fluorescence microscope. The most fundamental components of FISH are the targeted DNA sequence and the DNA probe. Before hybridization can take place, the DNA probe must be labeled using various means, for example: random primer labeling, nick translation, or polymerase chain reaction. Two different strategies can be used for labeling: the direct method and the indirect method. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get the original essayIn indirect labeling, the DNA probe is labeled with a modified nucleotide that contains a hapten, while indirect labeling of nucleotides that have been directly modified to contain a fluorophore are used. These fluorescently labeled probes, i.e. FISH probes, are first denatured, then the combination of the denatured probe and the target sequence allows the complementary DNA sequences to hybridize. For indirectly labeled probes, an additional step is required to visualize the non-fluorescent hapten which often uses an enzymatic/immunological detection system. Although FISH is faster with the use of directly labeled probes, indirect labeling has the advantage of intensifying the signal using many antibody layers, and thus, brighter signal production can take place compared to at background levels. Due to its ability to detect chromosomal aberrations such as gene rearrangement, gene deletion and gene amplification and its high specificity; FISH procedures are widely used in molecular diagnostics to detect and identify: Centromeres of a specific chromosome. Specific oncogenes (locus specific probe, useful for (ROS1, ALK), amplifications (HER-2), deletions (CLL) etc.). Specific tumor suppressor genes (locus specific probe, loss is relevant to tumor progression) Whole chromosomes (useful for detection of complex chromosomal rearrangements). FISH procedures are typically performed on FFPE (formalin-fixed paraffin-embedded) tissue preparations or cell preparations. . The advantages of FISH analysis over conventional chromosome analysis include: Keep in mind: This is just one sample. Get a personalized document from our expert writers now. Get a custom assay Large numbers of cells can be examined (useful for detecting residual disease) Metaphase cells are not essential, so aberrations can also be detected in non-dividing cells (beneficial in lymphocytic leukemia chronic) FISH can be performed in a relatively short period of time. Aberrations, too subtle to be detected by the use of conventional cytogenetic analysis, may also be identified. Most FISH procedures are performed in the dark to avoid photobleaching (the probes are very sensitive to light). FISH slides are observed under a fluorescence microscope equipped with probe-specific excitation and dichroic filters. The FISH procedure, as performed during the internship, is as follows: Incubate the FFPE.