Fig. 7.

Chromatin expansion and contraction in meiotic prophase. (A) Chromatin volumes and sister chromatid cross-section morphologies seen by optical sectioning of maize leptotene and zygotene nuclei (25). (B) Pachytene chromosomes of Locusta migratoria (source, G.H.J). (C) Chromatin of human oocyte nuclei visualized by EM in ultrathin sections (26). At late zygotene/early pachytene, chromatin is highly condensed, leaving clear chromatin-free areas within the nucleus; at midpachytene, chromatin masses are less dense, and chromatin is more evenly distributed; compact chromatin returns at late pachytene; and less dense chromatin then returns at “the diffuse stage.” (D) Immunostaining of histone H3 Ser-10 phosphorylation at successive stages of meiotic leptotene/zygotene in Sordaria (source, D.Z.; Fig. 11). [A and C are reprinted with permission from, respectively, ref. 25 (Copyright 1994, Elsevier) and ref. 26 by courtesy of the Carlsberg Laboratory (Copyright 1970, The Carlsberg Laboratory, Copenhagen).]