Figure 1.

ChIP-chip. Regions of interest on DNA are densely tiled, with probes separated by short distances. In this figure, each bar corresponds to the log-ratio hybridization signals of two channels measured by a probe. Small sub-regions that are over-represented compared to the genomic background will appear as pronounced peaks (in this example, the middle peak represents the DNA fragments containing a protein-binding site). The computational challenge is to normalize the data properly and to detect confident enriched regions by filtering out false peaks (left and right peaks in this example).