Nuclear architecture of spermatocytes 2n=24. a Distribution of metacentric and telocentric bivalents in a 3D pachytene nucleus from 2n = 24 spermatocytes. The synaptonemal complexes (green) and centromeres (red) were identified by immunochemistry using anti-SYCP3 and anti-CENPA antibodies. The metacentric bivalents form SCs longer than those of the telocentric bivalents and the centromeres are localized in the middle of the metacentric bivalents unlike the terminal position in the telocentric bivalents. The focus is over one metacentric Rb bivalent. Bar = 5 μm. b. Scheme representing the nuclear architecture of 2n = 24 spermatocytes. The centromeric regions of the three telocentric bivalents (T) are located at the nuclear periphery and the centromeric regions of the metacentric bivalents at the nuclear center. The associations are produced mostly within groups of telocentric or metacentric bivalents. The XY chromatin is also respresented (blue). c &d Associations between metacentric and telocentric bivalents through heterochromatin in 2n = 24 spermatocytes. The SC (green) and the pericentromeric heterochromatin (red) were identified by immunochemistry using anti-SYCP3 and anti-H3K9me3 antibodies. The associations were mainly between the telocentric or the metacentric bivalents. c) Nucleus with 6 associated metacentric bivalents and 2 singles; the 3 telocentric bivalents appear all together. The XY bivalent is indicated. d) Nucleus with three groups of metacentric bivalents: 4 associated, 2 associated and 1 single; the 3 telocentric bivalents appear all together. The XY bivalent is indicated.