Nuclear architecture of spermatocytes 2n=40. a Distribution of telocentric bivalents in a 3D pachytene nucleus from 2n = 40 spermatocytes. The synaptonemal complexes (green) and centromeres (red) were identified by immunochemistry using anti-SYCP3 and anti-CENPA antibodies. The 19 autosomal bivalents form regular arcs with the centromeres (red) (and the heterochromatin) in one extreme of each and consequently localized at the nuclear periphery. The focus is over one telocentric bivalent. Bar = 5 μm. b Scheme representing the nuclear architecture of 2n = 40 spermatocytes. The centromeric regions (red) of all telocentric bivalents are located at the nuclear periphery. The bivalentes can be alone or associated in different numbers. The XY chromatin is also represented (blue). c & d. Associations between telocentric bivalents through heterochromatin in 2n = 40 spermatocytes. The SC (green) and the pericentromeric heterochromatin (red) were identified by immunochemistry using, respectively, anti-SYCP3 and anti-H3K9me3 antibodies. XY = sex bivalent. The19 autosomal bivalents appear singly or associated in different numerical combinations per spermatocyte. The combinatory presents in the nucleus of figure c) is: 5-4-3-2-2-2-1 = 19; and in the figure d) is: 6-3-2-2-2-1-1-1-1 = 19.