Arrays

A DNA array is a collection of spots attached to a solid support such as a microscope slide; each spot contains one or more DNA oligonucleotides. Arrays make it possible to put down a large number of very small (100 micrometre diameter) spots on a single slide; if each spot has a DNA molecule that is complementary to a single gene (similar to Southern blotting), one can analyze the expression of every gene in an organism in a single expression profiling experiment . For instance, the common baker's yeast, Saccharomyces cerevisiae, contains about 7000 genes; with a microarray, one can measure quantitatively, how each gene is expressed, and how that expression changes, for example, with a change in temperature. There are many different ways to fabricate microarrays; the most common are silicon chips, microscope slides with spots of ~ 100 micrometre diameter, custom arrays, and arrays with larger spots on porous membranes (macroarrays).
Arrays can also be made with molecules other than DNA. For example, an antibody array can be used to determine what proteins or bacteria are present in a blood sample.