a, Chromosomes at the CO-designation stage (late leptotene), well-visualized in the filamentous fungus Sordaria, suggest that the axis (illuminated with Spo76-GFP) incorporates a significant fraction of chromatin (stained with DAPI) in a DNA/protein structural meshwork (images by D. Zickler). b, Model. (top): Global chromatin expansion within the structural axis meshwork is constrained by meshwork tethers, giving an expanded, mechanically stressed meshwork state. (bottom): Spreading interference creates a more contracted state with resulting reduction in mechanical meshwork stress. Full implementation of contraction, and thus maximal spreading of interference, requires readjustment of spatial relationships among component DNA segments which, comprising topologically closed domains, require TopoII-mediated duplex/duplex passages (yellow stars).