Locations of the ageing-associated methylation sites identified in the nonagenarians. Ageing-associated hyper- and hypomethylated probes are distributed differently across the genome. The distribution of ageing-associated CpGs in relation to (a) genes and (b) CpG islands. Ageing-associated hypermethylation is mainly located in CpG islands, TSSs and the 1st exons of genes, whereas ageing-associated hypomethylation occurs mainly in non-CGIs, gene bodies and areas outside of genes. In the figure, array denotes the distribution of probes in the 450K array.