Figure 1. Infinium 450k probes classification and BOPs definition. (A) The 485577 probes included in the Illumina HumanMethylation450 BeadChip were divided in 4 classes on the basis of their genomic localization. (B) Graphic representation of how probes were grouped in BOPs. Probes mapping in the island and in the surrounding regions of the same CpG island were grouped in 5 functional units: probes in the N-Shelf of the island, probes in the N-Shore of the island, probes in the island, probes in the S-Shore of the island, probes in the S-Shelf of the island. Probes mapping in gene bodies were grouped on the basis of the gene in which they are located.