Fig. 5. (A-B) Electron micrographs of two consecutive sections of a mid-late pachytene spermatocyte. Sex chromatin has higher electron density than the rest of the chromatin. The sex body is associated with the nuclear envelope (NE). An axis (Ax) emanates from the NE showing an expansion at its base (arrowheads). A layer of electron-dense material corresponding to the dense plate (DP) (arrow) is present on the nucleoplasmic side of the NE. The DP has a granular structure and is continuous with the axis (Ax). The centrioles (Cen) and Golgi (G) are adjacent. (C-E) Electron micrographs of XY pairs from three different spread pachytene spermatocytes. (C) Early pachytene. The AEs are thickened. The AE of the X chromosome shows an irregular outline, with expansions at its ends and in the centromeric region (arrow). The AE of the Y chromosome is less distinct. (D) Mid pachytene. Both AEs are more elongated and thinner than in previous stages. An electron-dense material is present at the ends of AEs (arrowheads). It is composed of fine threads that extend from one extreme to the other. The centromere knob of the X chromosome is visible (arrow). (E) Late pachytene. The sex chromosomal AEs do not touch each other. An electron-dense material, the balloon (BL), mediates the association of AE ends. Bars, 0.5 µm in A,B; 1 µm in C,E.