By Levi Clancy for Student Reader on
DNA microarrays consist of glass or silicone chip with thousands or hundreds DNA segments (called reporters) affixed to it. A DNA microarray can be used to assay transcription and to determine gene function, and to make comparisons between similar strains of cells.
For example, RNA from brain tumor cells can be compared to RNA from healthy brain cells. Reporters binding RNA in the tumor sample but not in the healthy one may indicate genes associated with disease. The two samples' cDNA are tagged with 2 colors, enabling comparison on a single chip. This is called expression analysis even thought the RNA might not be translated. Gene chip, DNA chip, chip, cDNA or oligonucleotide microarray.
Fluorescence intensity is proportional to number of copies of a particular mRNA present, and thus indicates expression level of that gene. Arrays can paint a picture or "profile" of which genes in the genome are active in a particular cell type and under a particular condition. See Southern Blotting.