CpG dinucleotides and methylated DNA centered at the DMD. A,B,C. The distribution of A, T, C and G over the 220 kb cluster show that there is a predominant accumulation of cytosines over the DMD and repeat region. The DMD repeat region has large amount of C and G together. There are two CpG islands in the region: one, which is the DMD and the other, which is in the promoter region of Rasgrf1 (bottom panel). D. Southern blot analysis of the two CpG islands using methylation sensitive restriction enzymes and tail DNA show that there is monoallelic methylation at the DMD (left panel) but no methylation of the promoter region CpG island (right panel). P (PstNI), N (NotI, methylation sensitive), E (EcoRI), Br (BsrBI, methylation sensitive). Bands diagnostic for the methylated (+) and unmethylated (−) states are indicated. (0.55 MB TIF)