Fig. 1

Post-meiotic sex chromatin. a Immunofluorescence pictures of a round spermatid nucleus stained with DAPI (left in black and white; right in blue) and with an X chromosome paint (pink). The bright DAPI-dense region is the chromocenter; the arrow indicates the adjacent DAPI-dense region in which the X chromosome is located. A similar pattern is observed with a Y chromosome paint [24–26, 34]. b Schematic diagram of XY gene expression during mouse spermatogenesis (adapted from [37]). In spermatogonia, X and Y gene expression is comparable to that of autosomes. At the pachytene stage of meiosis I, XY genes are transcriptionally shut down by MSCI (meiotic sex chromosome inactivation). After meiosis, XY gene expression is reactivated. The timing of appearance of the chromatin marks enriched on the sex chromosomes (as observed by immunofluorescence) during and after meiosis is represented under the schematic diagram. c Representation of the size of the mouse sex chromosomes in mm9/NCBIM37 (April 2007) and in mm10/GRCm38 (January 2012). In mm9/NCBIM37, the X and Y chromosomes are, respectively, 166.7 and 16 Mb, while in mm10/GRCm38 the X and Y chromosomes are, respectively, 171 and 91.8 Mb. Adapted from Ensembl http://www.ensembl.org/index.html