Figure 1.

Schematic of an Affymetrix probe (209649_at PM₅, left) bound with complementary target sequence (right). DNA double helix represented as straight vertical ladder. Note complementary T-A and C-G base bindings are shown by red rectangles. The 25 bases of the probe are tethered to the slide by a flexible linker (black lower left). Firmly bound target sequences can be detected by treatment with a florescent dye, whose location is detected with a laser and an optical microscope. The florescent intensity is approximately proportional to the amount of bound target and so gives some indication of target gene activity.