Fig. 3. Double immunolabelling on spread primary spermatocytes with anti-SCP1 (green) (A-C) and anti-SCP3 (red) (D-F) sera. (G-I) Enlargement of the sex chromosomes shown in A-F, where the anti-SCP1 and anti-SCP3 labelling have been superimposed and appear yellow where they colocalise. (A,D) Zygotene spermatocyte where synapsed autosomal regions are labelled with both SCP1 and SCP3 (arrows in A and D), whereas unsynapsed autosomal and sex (XY) AEs are only labelled with anti-SCP3 (arrowheads in D). (G) Enlargement of the sex chromosomes shown in A and D. The end of an autosomal SC appears yellow, whereas the unsynapsed sex chromosomal AEs, associated by one of their ends (arrowhead), only show red labelling corresponding to anti-SCP3. (B,E) Mid pachytene spermatocyte. Autosomes are fully synapsed as indicated by colocalisation of anti-SCP1 and anti-SCP3 labelling. (H) Detail of the sex chromosomes shown in B and E where they are associated by an anti-SCP3-positive structure (arrowhead) that is not labelled with anti-SCP1. (C,F) Late pachytene spermatocyte. Autosomes are fully synapsed. (I) Detail of the X and Y association shown in C and F. The anti-SCP3 positive plate (arrowhead) maintains the association between the sex AEs but no anti-SCP1 labelling is present. Bar, 10 µm in A-F; 2 µm in G-I.