DNA microarray: Difference between revisions

Revision as of 17:24, 27 September 2004

Revision as of 17:34, 27 September 2004

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Increased or decreased fluorescense intensity indicates that cells in the sample have recently transcribed,or ceased transcription, of a gene that contains the probed sequence ("recently," because cells tend to degrade RNAs soon after transcribing them). The intensity of the fluorescense is roughly proportional to the number of copies of a particular mRNA that were present and thus roughly indicates the ''activity'' or ''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.

Because many proteins have of unknown functions, and because many genes are active all the time in all kinds of cells, researchers usually use microarrays to make comparisons between similar cell types. For example, an RNA sample from [[brain tumor]] cells, might be compared to a sample from healthy [[neuron]]s or [[glia]]. Probes that bind RNA in the tumor sample but not in the healthy one may indicate genes that are uniquely associated with the disease. Typically in such a test, the two sample's cDNAs are tagged with two distinct colors, enabling comparison on a single chip. Researchers hope to find molecules that can be targeted for treatment with drugs among the various [[protein]]s encoded by disease-associated genes.

Although the chips detect RNAs that may or may not be translated into active proteins, scientists refer to these kinds of analysis as [[gene expression|"expression analysis"]] or [[expression profiling]]. Since there are hundreds or thousands of distinct probes on an array, each microarray experiment can accomplish the equivalent of thousands of genetic tests in parallel. Arrays have therefore dramatically accelerated many types of investigations.