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. 2021 Apr 7;118(15):e2017176118. doi: 10.1073/pnas.2017176118

Fig. 6.

Fig. 6.

Expanded features of axolotl mitotic chromosomes. (A) Mitotic chromosome heatmap. Hi-C map of chromosome arm 6q during mitosis. The inset demonstrates the presence of the secondary diagonals, which is characteristic for mitotic Hi-C heatmaps (scale bar 100 Mb). (B) Contact probability plots. Genome-wide contact probability plots are presented versus genomic distance between loci normalized to the contact probability at 10 Kb. In mitotic chromosomes (Bottom), the peak at 35 Mb (dashed line) corresponds to one turn of the helix. The peak in the first derivative (right) at 600 Kb corresponds to the length of a single loop within that turn. (C) Proposed model of helical organization of mitotic chromosomes. During mitosis, the DNA is packaged in ∼600 Kb loops, which themselves are arranged into helical turns of the polymer. A single turn comprises ∼35 Mb DNA, which agrees well with the values observed in the contact probability plot.