Comparative Genomic Hybridization (CGH) 

Comparative genomic hybridization (CGH) is a molecular cytogenetic technique designed to measure DNA copy number changes such as the gains or losses of specific DNA regions often observed in tumor cells. In CGH, two probe pools, one derived from tumor DNA, the other from normal DNA fragments, are labeled with two different fluorochromes, mixed and hybridized to normal metaphase chromosomes. Localized gains or losses of DNA result in increased or decreased fluorescence intensity along a chromosome.

CGH is a sensitive method and can detect quantitative chromosomal changes with high resolution, especially when applied in a microarray format. It is then sometimes referred to as Chromosomal Microarray Analysis (CMA). CGH detects rearrangements resulting in a net loss or gain of specific regions. However, it cannot reveal polyploidy changes (increase in number of the entire chromosome set) or chromosomal aberrations in which the total DNA amount remains the same, such as balanced translocations or inversions. Such chromosomal rearrangements can be visualized by Spectral Karyotyping.