In the conventional spotted glass microarray protocol, differences in RNA transcript abundance are measured as gene expression ratios between two RNA samples. In the example above, total RNA is isolated from yeast cells grown in two different media conditions, rich medium with either glucose or galactose as a carbon source. Each sample is then converted to cDNA and labeled with a different color fluorophore (Cy5 or Cy3). The labeled samples are pooled together and co-hybridized to the same array. In the example above, three genes known to be highly expressed in the galactose condition appear green in the false color overlay. Red features indicate higher expression on the glucose condition and yellow features indicate equally expressed levels.