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In cytogenetic analyses the chromosomes of certain body cells are examined under a light microscope. Aim of this investigation is the proof or exclusion of a numeric or structural conspicuous set of chromosomes (karyotype).
A conventional cytogenetic analyses consists of a production of metaphase preparations which contain cultures of patient cells and a following numeric and structural analyses of chromosomes according to a differential chromosome banding techniques. The most common differential chromosome banding technique is the GTG-banding, which allows a unique identification of each pair of chromosomes as well as a fine structure analyses. This method makes a chromosomal aberrations with relatively low resolution (ca. 10Mb) possible. The sortet presentation of chromosomes according to a differential chromosome banding technique is called Karyogram.
Molecular-cytogenetic methods such as the FISH-Analysis (fluorescence in situ hybridisation) allow an investigation of certain chromosomal areas with a distinctly higher resolution. Their application requires a specific diagnosis which is the result of the clinical symptomatology of the patient. Often molecular-cytogenetic analyses are also necessary to characterize or confirm a previously detected aberration. Furthermore molecular-cytogenetic methods allow an analysis on interphase cores. This is advantageous in issues which do not require dividing cells as a precondition. For this the prenatal rapid test in prenatal diagnostics serves as an example.
Array-CGH constitutes a special case among the molecular-cytogenetic methods. It enables high-resolution investigations of the human genome and is not depending on proliferating cells. It is only possible to detect genomic profit and loss with Array-CGH. Balanced chromosome aberrations such as translocations and inversions cannot be detected with this method. For a more accurate description see also Array-CGH.