Synaptonemal complex formation and distribution of recombination nodules in pachytene trivalents of triploid Coprinus cinereus

Abstract

Synaptonemal complex formation and distribution of recombination nodules were analyzed in trivalents of triploid Coprinus cinereus. The analysis of 14 completely reconstructed nuclei covering the period from early pachytene to mid diplotene has permitted the following conclusions: at pachytene, chromosome pairing and synaptonemal complex formation were almost exclusively in the form of trivalents. All three homologues were frequently associated at the same site, two central regions combining the three lateral components. The three homologues were never paired with three central regions. The trivalent configurations were maintained unaltered throughtout pachytene and at least the centromeres remained associated at early and mid diplotene. At mid-late pachytene, unpaired chromosome arms were frequently associated with central region material in some cases containing recombination nodules. The free face of such central regions was occasionally bound to an electron dense rod resembling a lateral component. Both central regions of the double complexes in the trivalents were able to bind recombination nodules. An analysis of the distribution of recombination nodules along the trivalents indicated that nodules were distributed independently between the two central regions of the trivalents.