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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