The schematic pictorial is showing that how a DNA microarray is constructed and used. It happens in three different steps which involves:

1. Preparation of the cDNA Probe in which mRNA samples are isolated from two different types of cells or tissues such as cancer cells and normal cells. Then enzymes are used to prepare complementary DNA molecules (cDNA) from both groups of mRNA. Contrasting fluorescent labels are attached to both groups of cDNA (red to cancer cells and green to normal cells).
2. Preparation of microarray happens by binding DNA corresponding to different genes fragments to the wells in a microarray plate. Single strands of DNA are attached to wells in the plate.
3. Combining the probe and microarray samples. Here labeled cDNA molecules are bound to complementary sequence of microarray on the plate.