SYNAPTONEMAL COMPLEXES - STRUCTURE AND FUNCTION

Synaptonemal complexes (SCs) are zipper-like structures which are asse mbled between homologous chromosomes during the prophase of the first meiotic division. Their assembly and disassembly correlate with the su ccessive chromatin rearrangements of meiotic prophase, namely the cond ensation, pairing, recombination and disjunction of homologous chromos omes. It was originally thought that SCs created the preconditions for the homologous crossing over of chromosomes by bringing corresponding parts of homologous chromosomes in close apposition. However, this vi ew has been gradually undermined during recent years, and ideas about the roles of SCs have radically changed. SCs are now considered to be structures that both control the number and distribution of reciprocal exchanges between homologous chromosomes (cross-overs) and convert cr oss-overs into functional chiasmata. How SCs fulfil these roles remain s to be elucidated.