ABSTRACT
Since microarrays were first described over 10 years ago [1], they have evolved into a standard, though still relatively expensive, experimental technology that has had a profound impact in molecular biology. Microarrays exploit preferential binding of DNA or RNA to their complementary single-stranded sequences. A microarray chip consists of thousands of single-stranded DNA molecules attached in fixed locations onto a solid surface. The microarray chip is incubated with a biological extract (mRNA or cDNA) that is labeled with a fluorescent dye. Thus a single microarray experiment produces thousands of data points, each of which is a measure of the quantity of fluorescent label bound at a feature on the microarray chip. These fluorescent intensities are indirect estimates from which the concentrations of mRNA
molecules are inferred. Tens of thousands of features can be fixed to a single microarray chip, thus providing an opportunity to quantify thousands of gene transcripts, indeed the entire human transcriptome in a single experiment. Knowing the presence or absence of transcripts for all the genes in the genome at a particular moment, and their changes relative to some reference state, is extremely valuable information, and these detailed transcriptomic portraits provide hitherto unimaginable insights into the regulation of biological processes in the cell.
