In Situ Hybridization - ISH,Fluorescence in Situ Hybridization (FISH)

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	In Situ Hybridization - ISH - The position of a particular gene on the cytological map of an organism can be determined directly with in situ hybridization (ISH). A radioactive probe representing a gene (a labelled cDNA clone derived from the mRNA) is hybridized with the denatured DNA of the polytene chromosomes in situ. The position or positions of the corresponding genes can be identified by autoradiography.
Fluorescence in situ hybridization (FISH) enables us to perform specific detection of unique sequences of varying length, chromosomal regions or entire chromosomes within metaphase or interphase cells, and rapid mapping and ordering of DNA fragments on single metaphase chromosome bands. A modification of this method is genomic in situ hybridization (GISH) which is used to identify alien chromatin in chromosome spreads.