The synaptonemal complex in chromosome pairing and disjunction

Abstract

A precise pairing of homologous chromosomes is an essential prerequisite for the ultimate success of meiosis, i.e., the formation of gametes each containing one balanced genome. In eukaryotes pairing between homologous chromosomes or chromosome segments is mediated by the synaptonemal complex, which ensures that the homologous segments are held in register for a certain period of time — the pachytene stage (Westergaard and von Wettstein 1972). At this and the previous zygotene stage, the synaptonemal complex serves as a vector for meiotic recombination by its association with recombination nodules (Carpenter 1975) and has been assigned a function in the regulation of the frequency and distribution of crossovers at pachytene (Holm and Rasmussen 1983a and b). The synaptonemal complex is essential at late meiotic prophase since retained synaptonemal complex segments appear to be universally present at the crosssover sites during the early part or most of the diplotene-diakinesis period (Holm and Rasmussen 1983b).