A Gene chip is not much larger than a coin. It is based on a glass substrate wafer and contains many tiny containers arrayed in a grid pattern. Some chips carry up to 400,000 of these miniature reaction wells, each of which contains a fragment of the genetic information strand DNA.

With the aid of gene chips, genome researchers can now investigate many hundreds of genes (protein blueprints) at the same time and can determine which genes are presently activated in a certain tissue.

The tiny nozzles of fine needles in a pipette robot inject a small droplet into each of the miniature reaction wells. The droplets contain messenger RNA strands which have previously been isolated from a cell or a certain tissue. These messenger RNA strands are “transcripts” of those genes which are to be converted into proteins within the cells. If the messenger RNA finds a DNA fragment with a similar sequence of “base letters”, the two strands connect to each other. Unattached messenger RNA is flushed away.

The messenger RNA is marked with coloring which flashes in the light of a laser. The light spots in the miniature reaction wells indicate where a messenger RNA has connected to a fitting DNA fragment. It is evident from the pattern and color of the light signals which messenger RNA fiber strands have been produced in a cell. And this makes it possible to conclude which and how many proteins are produced in a certain cell or in a certain tissue.

Gene-chips are used to compare normal and diseased tissues and to investigate, which Genes are involved in disease processes. The hope is that it will soon be possible for doctors to use the gene chips to run simple tests on patients in order to diagnose diseases with a genetic base or to find a tailored treatment.