Fig. 2.

Zygotene. At zygotene, homologous chromosomes (dark and light blue lines that represent double-strand DNA wrapped around histones) have paired and the synaptonemal complex (SC) starts to assemble. The SC consists of three parts: lateral elements, central region, and central element. The lateral elements (light purple) assemble alongside the axial elements (green) and cohesins (maroon rings). The central region contains the transverse filament proteins (red and orange), which span the distance between the two homologs and interact with the lateral elements. The central element (pink) contains a group of proteins that are thought to help to stabilize the middle of the SC. Although many of the steps of DSB repair are thought to occur during pachytene, some of the repair processes are initiated in zygotene. The dashed-circle region indicates a region where the single-strand DNA (ssDNA) coated in RAD51/DMC1 recombinase proteins (purple) is initiating DSB repair. The DSB is represented by the yellow star