Fig. 1: AFM imaging of native human mitotic chromosomes.

a AFM topography of a single native human mitotic chromosome imaged within PA buffer. b AFM topographical image zooming in the area within the blue dashed square reported in (a); blue arrows point to loop structures stemming from the central part of each chromatid while white arrows indicate chromatin fibers not arranged in loop-like structures. c Inset from (b) displaying different types of SCIs holding together the two sister chromatids; the upper arrow points at two loops interlaced together, while the lower one shows that multiple chromatin fibers are still connected with both sister chromatids. d Schematic representation of (c), highlighting the two types of SCIs and two randomly coiled fibers. e The inset shows a high-contrast image of the area within the green dashed square in (a), in these conditions, it is possible to see the halo of chromatin surrounding the chromosome (full picture in Fig. S1). The histogram describes the height distribution of the chromatin halo, fitted with a combination of 5 Gaussian curves (the minimum number that yielded an accurate fit). f Illustrative height profile (red trace) describing the height fluctuations of the chromosome surface (gray structure is a 2D simplified representation of loops making up the chromosome body). The horizontal dashed black line indicates theN mean surface height. The standard deviation (\({\sigma }_{L}\)) characterizes the surface roughness. The magnitude of \({\sigma }_{L}\) depends on the sampled length scale \(L\). g Averaging all the values of \({\sigma }_{L}\) along different longitudinal profiles yields a measure of the average surface roughness\(\,{\sigma }_{L}\); repeating the procedure for different length scales L reveals a power-law scaling regime (dashed red line), indicating self-affinity.