a G-banded sex chromosomes in the male common shrew (left) and ideogram with chromosome arms labelled according to the alphabetic nomenclature of Searle et al. (1991)b Schematic diagram of the shrew pachytene sex trivalent, based on Pack et al. (1993) and our data c Electron micrograph of a shrew sex trivalent, XY1Y2 at late pachytene. The true X region and the Y1 are surrounded by electron-dense material. Scale bar: 5µm. d Diagram of the XY1Y2 configuration as represented in Fig. 1c.