Demystified ... Comparative genomic hybridisation

Comparative genomic hybridisation (CGH) is a technique that permits the det ection of chromosomal copy number changes without the need for cell culturi ng. It provides a global overview of chromosomal gains and losses throughou t the whole genome of a tumour. Tumour DNA is labelled with a green fluoroc hrome, which is subsequently mixed (1:1) with red labelled normal DNA and h ybridised to normal human metaphase preparations. The green and red labelle d DNA fragments compete for hybridisation to their locus of origin on the c hromosomes. The green to red fluorescence ratio measured along the chromoso mal axis represents loss or gain of genetic material in the tumour at that specific locus. In addition to a fluorescence microscope, the technique req uires a computer with dedicated image analysis software to perform the anal ysis. This review aims to provide a detailed discussion of the CGH techniqu e, and to provide a protocol with an emphasis on crucial steps.