Human meiosis IV. The elimination of synaptonemal complex fragments from metaphase I bivalents of human spermatocytes

Abstract

Three dimensional reconstructions of 3 prometaphase 1, 6 methaphase 1 and 2 anaphase 1 cells from 4 normal human males have been performed. At prometaphase I, 45, 36 and 32 fragments of synaptonemal complexes are present, of which 42, 22 and 23 were located within the bivalents. At metaphase I, the synaptonemal complex fragments are expelled from the bivalents, either as apparently intact fragments or as rearranged subunits of the synaptonemal complex which form small synaptonemal polycomplexes at the border of the bivalents or in the nucleoplasm. At early anaphase I, the bivalents were almost completely devoid of synaptonemal complex fragments. The possible relationship between these fragments and chiasmata is discussed. The changes in the ultrastructure of the bivalents during these stages is described. At prometaphase each of the four chromatids of a bivalent possesses a kinetochore.