Presynaptic stages in V. berus primary spermatocytes. (a) Leptotene, long axial elements are completely asynapted, centromeres distributed over all spread nuclei. (b) Chromosomal ‘bouquet’ stage, U-shaped axial elements of chromosomes, clusterization of telomere ends in the local region of the spread nucleus. (c) Mid zygotene, asynchronous synapsis of the long chromosomes and microchromosomes. MLH1 protein loaded in bivalents of microchromosomes as well as in the regions of local synapsis of long assembling bivalents. (d) Late zygotene, finalization of assembly of the long bivalents. Bivalents of microchromosomes are fully assembled. Heterochromatin region on the chromosome pair 6 is indicated as HR6. AE—axial elements of asynapted chromosomes. SC—assembled regions of synaptonemal complexes. Axial elements of chromosomes are immunostained with antibodies against the SYCP3 protein (green), centromeres with antikinetochore antibodies ACA (yellow). Mismatch repair protein sites are immunostained with antibodies against MLH1 protein (red). Chromatin stained with DAPI (blue). Bar—10 μm.