Leptotene oocytes of hybrids appeared normal with assembling lateral elements of SC labeled by RAD51 (Fig. 2a). At zygotene, lateral elements established contacts with each other while the central elements formed asynchronously. Thus, while some lateral elements were already paired, others displayed extensive asynapsis. Asynaptic regions were often intertwined and labeled by RAD51 and γH2A.X (Fig. 2b,c, Fig. S2). Some regions kept these marks until pachytene when most autosomes were synapsed (Fig. S2).