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Molecular Pathology


Variations - Comparative genomic hybridization


Author: Rodney E. Shackelford, DO, Ph.D. (see Reviewers page)

Revised: 3 July 2010, last major update July 2010

Copyright: (c) 2008-2010, PathologyOutlines.com, Inc.




Comparative Genomic Hybridization (CGH) is used to detect copy number changes (amplifications or deletions) of relatively large genomic segments

CGH only detects unbalanced chromosomal changes; balanced chromosomal alterations, such as inversions and translocations are not detected, as no change in copy number occurs




● Control DNA is taken from cells with a normal karyotype and compared to the sample to be examined

The examined sample is often from a tumor or tissue from a child with dysmorphic features who is likely to have unknown genomic amplifications or deletions

Originally, CGH was done with fluorescent-labeled metaphase chromosomes immobilized on glass slides, co-hybridized with different fluorescent-labeled control and sample DNA

Comparison of the different preparations and fluorescent labels allows the identification of changes in the copy number along specific chromosomal regions

The resolution of this approach is low, allowing only changes of 20 Mb or more to be identified (DNA Microarrays for Biomedical Research: Methods and Protocols; Humana Press, 2009)

● Currently array CGH is more commonly used to analyze amplifications or deletions between sample and control cells; it uses an immobilized probe array, to which are hybridized differently labeled normal and sample DNAs; the resolution depends upon the number of immobilized probes employed

CGH allows only the comparison of the relative ratio of different DNA segments between samples and controls, not the ploidy; thus, comparing two tetraploid clones lacking amplifications or deletions by CGH would give a normal result


End of Molecular Pathology > Microarray > Variations > Comparative genomic hybridization



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