Methylation profiles of multiple tissues show striking differences. Cerebellum, heart, liver, lung, testis, and ovary are each profiled relative to spleen. With the exception of the ovary:spleen comparison, these representative plots were obtained using tissues from the same male donor. The log2 ratios for chromosome 1 clones are indicated at their relative genomic position, with the large gap representing the centromere and pericentromeric repeats in 1p11–1q21. The horizontal scale for the X chromosome is compressed; the 17 chromosome X clones on the array are actually distributed over 110 Mb. Clones highlighted in black have log2 ratios that deviate from the overall median, set here to 0, in either direction by >4.88 median absolute deviation (MAD) units, where MAD units are calculated using the data for the clones in the region of 1q marked 'MAD' (position 184 to 197 Mb), which showed the least biological variation within and across experiments. High log2 ratios are expected for regions hypomethylated relative to clones of similar GC content in the test tissue relative to spleen, whereas low log2 ratios are expected to represent relatively hypermethylated regions. In the heart-versus-spleen profile, bacterial artificial chromosome (BAC) RP11-47A4, containing part of the RYR2 gene, is highlighted in red and BAC RP11-90O23, containing part of ATP2B4, is highlighted in blue.