Fig. 2. Double immunolabelling on squashed primary spermatocytes with anti-SCP3 (green) and anti-centromere CREST (red) sera. (A-A') Single focal plane through an early pachytene spermatocyte. Sex chromosomes lie on the nuclear periphery. Five autosomal centromeres and the sex chromosomes centromeres are visible. X and Y short (Xp and Yp respectively) arms face each other. (B-B') Single focal plane of an early pachytene spermatocyte in which the sex chromosomes are in contact. Here the association is Xq-Yp and Xp-Yq (arrows). (C-C') A mid pachytene spermatocyte in which both X and Y long arms face each other (arrow). Bars, 5 µm in (A-C); 2 µm (A'-C').