Fig. 1

Molecular Clock vs Universal PaceMaker: Solid lines (colors) represent different methylation sites. Vertical (dashed) lines represent time points. Hence dots along dashed lines correspond to (log) methylation rates at that very time point of each methylation site. Under the Molecular Clock (MC) model (left), methylation rates of sites differ among each other but are constant in time. By contrast, under the Universal PaceMaker (UPM) model (right), rates may vary during with time but the pairwise ratio between sites rates remains constant (diference between log rates is constant)