Fig. 2.

a. Before synapsis, homologous chromosomes consist of chromatin loops (violet, gray) attached to an axial core. The size and extent of individual loops are not well-characterized. To allow synapsis, the loops of chromatin must somehow become oriented to allow intimate synapsis at a distance of <200 nm. b. When chromosomes have synapsed, chromatin is often visible as more densely packed and pushed to either side. The CE proteins polymerized between the axes are shown in one possible conformation consistent with the model in (Schild-Prüfert et al. 2011). c. Schematic of the two kinds of SC structure in barley visualized with 3D-SIM in Phillips et al. (2012). Models of alternate SC structure are taken from Phillips et al. 2012. In barley meiocytes, the SC was observed by 3D-SIM to exist both in a canonical one-level configuration (right) as well as a two-level configuration (left)