page_title: Molecular cytogenetics
section_title: Fluorescence in situ hybridization (FISH)
hierarchical_section_title: Molecular cytogenetics / Common techniques / Fluorescence in situ hybridization (FISH)
caption_attribution_description: Deutsch: DNA des menschlichen Chromosoms 2 wurde markiert, per Fluoreszenz in situ Hybridisierung auf Metaphase-Chromosomen des Orang-Utan (links) und des Menschen (rechts) gegeben und grün angefärbt. Während beim Menschen dadurch nur die beiden Kopien des Chromosoms 2 angefärbt wurden, wurden beim Orang-Utan die Kopien der beiden ursprünglichen Chromosomen markiert (siehe de:Chromosom #Chromosomenevolution ). Die restlichen Chromosomen sind durch eine DNA-Färbung rot gefärbt. Das menschliche Chromosom 2 setzt sich aus Teilen zusammen, die bei den Menschenaffen noch auf zwei Chromosomen verteilt sind. Die Fusion fand also nach der Trennung von den Schimpansen statt. Der Fusionspunkt liegt bei 2q13-14. English: DNA of the human chromosome 2 was labeled, applied to Orang-Utan (left) and human metaphase chromosomes (right) by fluorescence in situ hybridization and detected in green. While in the human metaphase spread only the two copies of chromosome 2 were detected, in the Orang-Utan metaphase spread the two original chromosome pairs were painted: Human chromosome 2 is the evolutionary derived fusion product from two separate ancestral chromosomes. In non-human primates - like for example in the Orang-Utan (chromosomes on the left side) - as well as in several other mammals, two chromosomes are observed which carry human chromosome 2 orthologous genes and syntenic segments of orthologous DNA sequences. The fusion in human 2q13-14 at approximately 114 Mbp of the human reference sequence (see Ensembl) occurred after the split of the human and chimpanzee lineages from that of their last common ancestor.
context_page_description: Molecular cytogenetics combines two disciplines, molecular biology and cytogenetics, and involves the analyzation of chromosome structure to help distinguish normal and cancer-causing cells. Human cytogenetics began in 1956 when it was discovered that normal human cells contain 46 chromosomes. However, the first microscopic observations of chromosomes were reported by Arnold, Flemming, and Hansemann in the late 1800s. Their work was ignored for decades until the actual chromosome number in humans was discovered as 46. In 1879, Arnold examined sarcoma and carcinoma cells having very large nuclei. Today, the study of molecular cytogenetics can be useful in diagnosing and treating various malignancies such as hematological malignancies, brain tumors, and other precursors of cancer. The field is overall focused on studying the evolution of chromosomes, more specifically the number, structure, function, and origin of chromosome abnormalities. It includes a series of techniques referred to as fluorescence in situ hybridization, or FISH, in which DNA probes are labeled with different colored fluorescent tags to visualize one or more specific regions of the genome.
context_section_description: Fluorescence In Situ Hybridization maps out single copy or repetitive DNA sequences through localization labeling of specific nucleic acids. The technique utilizes different DNA probes labeled with fluorescent tags that bind to one or more specific regions of the genome. It labels all individual chromosomes at every stage of cell division to display structural and numerical abnormalities that may arise throughout the cycle. This is done with a probe that can be locus specific, centromeric, telomeric, and whole-chromosomal. This technique is typically preformed on interphase cells and paraffin block tissues. FISH maps out single copy or repetitive DNA sequences through localization labeling of specific nucleic acids. The technique utilizes different DNA probes labeled with fluorescent tags that bind to one or more specific regions of the genome. Signals from the fluorescent tags can be seen with microscopy, and mutations can be seen by comparing these signals to healthy cells.For this to work, DNA must be denatured using heat or chemicals to break the hydrogen bonds; this allows hybridization to occur once two samples are mixed. The florescent probes create new hydrogen bonds, thus repairing DNA with their complimentary bases, which can be detected through microscopy. FISH allows one to visualize different parts of the chromosome at different stages of the cell cycle. FISH can either be performed as a direct approach to metaphase chromosomes or interphase nuclei. Alternatively, an indirect approach can be taken in which the entire genome can be assessed for copy number changes using virtual karyotyping. Virtual karyotypes are generated from microarrays made of thousands to millions of probes, and computational tools are used to recreate the genome in silico.
caption: FISH images of chromosomes from dividing orangutan (left) and human (right) cells. Yellow probe shows 4 copies of a region in the orangutan genome and only 2 copies in human.
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