FIGURE 1.

Chromosomal events in each stage of meiotic prophase I. A, Interactions between one pair of homologous chromosomes (red and blue) within a nucleus in each stage of prophase I are schematically represented. In the leptotene stage, the chromosomes begin to condense. In the following zygotene stage, synapsis begins with the formation of the synaptonemal complex (SC) (gray) between homologous chromosomes. In the pachytene stage, synapsis is completed and the SC is fully assembled. Crossing over of genetic materials also occurs in the pachytene stage. In the diplotene and diakinesis stages, the SC is disassembled and chiasmata resulting from interhomolog recombination become visible and serve to connect the homologs. B, Structures of the SC in each stage of prophase I are indicated. SC components progressively assemble to form the synaptic chromosome. In the leptotene stage, the axial elements (AEs), which will be termed lateral elements (LEs) in the next stage, assemble with cohesin and form the chromosome axis. In the zygotene stage, the LEs are formed from AEs, connected by the central region (CR) to form the SC. In the pachytene stage, the SC is fully assembled. The SC is a ladder‐like proteinaceous structure that is formed between two homologous chromosomes, and consists of two LEs (comprised of SYCP2 and SYCP3) and a CR that contains the central element (CE) (comprised of SYCE1, SYCE2, SYCE3, TEX12, and SIX6OS1) and the transverse filaments (TFs) (comprised of SYCP1). The SC is important for stabilizing homologous pairs and facilitating the completion of meiotic recombination