Friday, September 28, 2007

DNA microarray

A DNA microarray (also commonly known as gene or genome chip, DNA chip, or gene array) is a collection of microscopic DNA spots, commonly representing single genes, arrayed on a solid surface by covalent attachment to chemically suitable matrices.

DNA arrays are different from other types of microarray only in that they either measure DNA or use DNA as part of its detection system. Qualitative or quantitative measurements with DNA microarrays utilize the selective nature of DNA-DNA or DNA-RNA hybridization under high-stringency conditions and fluorophore-based detection. DNA arrays are commonly used for expression profiling, i.e., monitoring expression levels of thousands of genes simultaneously, or for comparative genomic hybridization.

Microarray technology is often used for gene expression profiling. It makes use of the sequence resources created by the genome sequencing projects and other sequencing efforts to answer the question, what genes are expressed in a particular cell type of an organism, at a particular time, under particular conditions?

For instance, they allow comparison of gene expression between normal and diseased (e.g., cancerous) cells. There are several names for this technology - DNA microarrays, DNA arrays, DNA chips, gene chips, others. Sometimes a distinction is made between these names but in fact they are all synonyms as there are no standard definitions for which type of microarray technology should be called by which name.

Microarrays exploit the preferential binding of complementary nucleic acid sequences. A microarray is typically a glass slide, on to which DNA molecules are attached at fixed locations (spots or features). There may be tens of thousands of spots on an array, each containing a huge number of identical DNA molecules (or fragments of identical molecules), of lengths from twenty to hundreds of nucleotides. The spots on a microarray are either printed on the microarrays by a robot, or synthesized by photo-lithography (similar to computer chip productions) or by ink-jet printing. There are commercially available microarrays, however many academic labs produce their own microarrays.

Microarrays that contain all of the about 6000 genes of the yeast genome have been available since 1997. The latest generations of commercial microarrays represent the entire human genome, more than 30,000 genes, on two microarrays.

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