Gene expression microarrays fluorescence signal

The raw data obtained from microarray analyses rarely remain raw for long. The data are simmered in a series of transformations needed to address basic questions of gene expression. Typical transformations include background subtraction, normalization, ratio calculations, and log transformation. The normalization is required because the scale for fluorescence emissions from different fluoro-phores are rarely equivalent. In addition, the scale for signal from the same fluorescent label... 

Several methods are available to monitor transcription levels of tens of thousands of genes rapidly and simultaneously. The quantification of RNA species by sequence-specific annealing (hybridization) to complementary DNA probes arrayed on a substrate (microarray) was developed by Schena etal. (1995). Sample RNA was submitted to reverse transcription and fluorescent labeling. Thereby, a quantitative parameter was produced that could be measured as a localized signal after hybridization to the arrayed sensors. Comparison by competitive hybridization of two RNA samples labeled with two different dyes (Cy3 and Cy5) resulted in expression ratios of the two sources (e.g., of tumor and nontumor tissue). Whereas sensors were originally taken from libraries of DNA clones (cDNA), present-day microar-... 

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