DNA microarrays (or DNA chips) have been the most commonly used technique during the last two decades to globally monitor the cellular abundances of transcript species. A DNA microarray is a collection of microscopic DNA spots attached to a solid surface. Each DNA spot contains many thousands of copies of a specific DNA sequence, known as probes. These usually correspond to a short section of a gene generally at the 3′ end. Each microarray contains one or a few probe sets for each interrogated gene. These are used to hybridize a cDNA sample (the target) under high-stringency conditions. Probe–target hybridization is usually detected and quantified by detection of fluorophore-, silver-, or chemiluminescence-labeled targets to determine the relative abundance of transcripts in the target sam