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Theory of the FISH method
Clinical applications (CATCH 22 syndrome)

With the somewhat expensive fluorescence-in-situ-hybridization (FISH) small, individual chromosome sections can be made visible. Today many different probes are available for these investigations. Such probes are utilized to search for individual sections (> 5 million bases) on the DNA. This technique is used in order to detect structural aberrations that are only inadequately displayed using classical chromosome banding techniques. It is, though, too coarse for analyzing individual gene defects.

FISH method

With this examination method short, individual chromosome segments can be made visible, in that they are hybridized with a fluorescent-labelled, complementary probe. This method is employed in the analysis of structural chromosomal aberrations, in constructing gene maps (gene mapping) and in the search for oncogeneoncogenes, so long as the sought-after chromosome segment is sufficiently large.
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A
B

2		 Probe DNA
The probe DNA is marked with a fluorescing dye.
Through denaturing, the double strand is opened and the
probe DNA hybridizes to a part of the chromosome.
Fluorescing bands on the chromosome are seen under the fluorescence microscope