A microarray or DNA chip is an assembly of
oligonucleotides or other DNA probes, e.g.,
cDNA clones, fixed on a fine grid of surfaces. It is
used to analyze the expression states of a series
of genes represented in cDNA prepared from
mRNA (expression screening) or to recognize
sequence variations in genes (screening for
DNA variation). The advantages of using microarrays
are manyfold: simultaneous large-scale
analysis of thousands of genes at a time, automation,
small sample size, and easy handling
given the right equipment. Several manufacturers
offer highly efficient microarrays that
can accomodate 300000 DNA probes on a highdensity
glass slide of small size (e.g.
1.28cm!1.28 cm).
Two basic types of DNA microarrays can be distinguished,
although many variations are being
developed: (i) microarrays of previously prepared
DNA clones or PCR products that are attached
to the surface, arranged in a high-density
gridded array in two-dimensional linear
coordinates; (ii) microarrays of oligonucleotides
synthesized in situ on a suitable surface.
Both types of DNA arrays can be hybridized
to labeled DNA probes in solution.
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