CGH

CGH (Comparative genomic hybridization) is FISH based method, which allows in one hybridization reaction detection of loses and gains in DNA sequences in the whole genome. It allows detection of chromosomal rearrangements, which lead to loses (monosomia, deletions) or multiplication (trizomia, amlification) of DNA.
==Method==
#isolation and quantification of the genomic DNA (from a test sample and a reference sample)
#labeling of the genomic DNA by Cy3 or Cy5 (test sample and reference sample with different colors)
#digestion of labeled DNA samples
#hybridization reaction- based on FISH technique, in which the whole genome DNA serves as a probe. 
#PC interpretation of data by measuring the level of fluorescence of the dies
==Disadvantages, advanatages:==
*detection of only unbalanced chromosomal aberations
*is not optimal for detection of ploidy
*limitations in resolution (resolution of classical CGH: 5-10Mb)
==Variants of CGH:==
===HR-CGH:===
High-resolution CGH has a better resolution (detection of abnormalities around 3Mb). In comparisson to classical CGH, it takes in account statistical information. Result are compared to profiles of control samples. HR-CGH is used for detecting microdeletion syndromes, small deletions and duplications
===Array CGH:===
Array CGH allows even higher resolution. Chromosomes are replaced by separated clones on a glass chip. Usage of BAC, PAC and oligonucleotides around 35kb.
Process: the patient and control DNA are labeled with fluorescent dyes and applied to an micro-array. The patient and control DNA compete to attach to the micro-array. The micro-array scans and measures fluorescent intensity.