Making DNA Probes From Cell Samples

First, the messenger RNA (mRNA) is extracted from the normal or unaffected cell sample, and a fluorescent-labeled cDNA probe is generated. The probe represents all of the genes expressed in these reference cells.

Next, the mRNA is extracted from another group of cells. Typically, these are the affected cells: exposed to a drug or toxic substance, taken from a tumor, or removed at a different time. The fluorescent labeling step is repeated to generate a second cDNA probe using a different color fluorescent molecule.

Applying Probes to the GEM Array

The two flourescent probe samples are simultaneously applied to a single microarray, where they competitively react with the arrayed cDNA molecules. Following incubation, the microarray is rinsed, washing off those probe molecules that did not find their cDNA counterpart.