DNA chips are small, solid supports such as microscope slides onto which th
ousands of cDNAs or oligonucleotides are arrayed, representing known genes
or simply EST clones, or covering the entire sequence of a gene with all it
s possible mutations. Fluorescently labeled DNA or RNA extracted from tissu
es is hybridized to the array. Laser scanning of the chip permits quantitat
ive evaluation of each individual complementary sequence present in the sam
ple.
DNA chip technology is currently being proposed for qualitative and quantit
ative applications, firstly for the detection of point mutations, small del
etions and insertions in genes involved irt human diseases or affected duri
ng cancer progression; secondly, to determine on a genome-wide basis the pa
ttern of gene expression in tumors, as well as in a number of experimental
situations.
The extraordinary power of DNA chips will have a strong impact on medicine
in the near future, both in the molecular characterization of tumors and ge
netic diseases and in drug discovery and evaluation Quantitative applicatio
ns will soon spread through all fields of biology.