Figure 4. Human Chr4 territories are less stable if the energy barrier against chain crossing is switched off.

The swelling from the initial “metaphase” configuration is monitored through the time behavior of the gyration radius [7], where r_l(t) is the position vector of the lth bead and r _cm(t) is the center of mass of the configuration at time t. Without barrier, chromosomes swell easier and have larger size (green and red lines, (A)). Comparison amongst internal distances between two sites located at N ₁ and N ₂ Mbp from one chosen end of the fiber and avalaible experimental data reflects this behavior (B). We have averaged over 3 time windows of exponentially growing size: 240 s<t<2,400 s (dark red line), 2,400 s<t<24,000 s (magenta line) and 24,000 s<t<240,000 s (cyan line). In particular, we notice that the fortuitous agreement of the magenta line with the data is lost due to the fast relaxation to equilibrium. The gray line corresponds to internal distances in the initial configuration. As expected (C), the final configuration of human Chr4 without energy barrier occupies a larger volume and is more random-walk-like than the ones where the energy barrier has been included.