DNA microarrays and Gene expression analysis

Expression analysis for the quantitative gene expression of many genes can be performed using either oneor two-colour fluorescent schemes. One-colour analysis is primarily used for arrays prepared by photolithography. Affymetrix ( http://www.affymetrix.com ) patented this process under the trade name GeneChipTM (Fodor, S.P.A. et al., 1995 ).In this method, expression profiles for each sample are generated on a different chip using a single fluorescent label, such as phycoerythin, and the different images are then compared. A two-colour analysis protocol has subsequently been developed, whereby two RNA samples are labelled separately with different fluorescent dyes, for example cyanine 3 and cyanine 5 (M. Schena et al., 1995) . These labelled probes hybridize to a printed array of cDNA; when the microarray is scanned, the fluorescent signals can be overlaid to visualize genes that have been activated or repressed.