Examples of cross-hybridization in two independent data sets. Magnitude versus amplitude (MA) plot of two arrays from the "Phage TAG array" (A) and the "Yeast TAG array" (B) data sets. The x-axis represents the average log2 intensity of the two channels, and the y-axis represents the log2 ratio of channel1/channel2. Probes identified as corruptors or corrupted in the first (R), the second (G) and both (RG) channels are highlighted with the respective labels. Horizontal lines indicate 2-fold change (log2 ratio = -/+1).