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"Microarray" refers not only to GeneChips but also to chips that use much longer probe sequences, such as the entire [[gene]]s that may be contained on [[cDNA]]s. Because, Affymetrix owns a [[patent]] both on the use of oligonucleotide probes as well as on a means to affix them to chips, microarrays not made by Affymetrix are manufactured by a different technique that is non-proprietary.
Typically arrays are used to detect the presence of [[mRNA]]s that encode different proteins. The RNA is extracted from many cells of a single type, then converted to cDNA and "amplified" in [[concentration]] by [[reverse transcriptase]]-[[PCR]]. [[Fluorescent tag]]s are chemically attached to the strands of DNA. A cDNA [[molecule]] that contains a sequence complementary to one of the single-stranded probes will stick via base pairing (more at [[DNA]]) to the spot on the array where the probe is affixed. The spot will [[fluoresceence|fluoresce]] (glow) when examined.
The glow indicates that cells in the sample were actively [[transcription|transcribing]] a gene that contained the sequence being probed. The intensity of the glow depends on how many molecules of a particular were present and roughly indicates the ''activity'' or ''expression level'' of a particular gene.
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