Femoral BM sections from BALB/c mice: (A) male, (B) female, (C) female 6 weeks posttransplant with 2,500 Rh/Hoe^dull marrow cells, and (E) female 6 weeks posttransplant with 100 × 10⁶ whole marrow cells. Sections are stained using in situ hybridization for a digoxigenin-conjugated Y chromosome-specific “painting” probe and rhodamine anti-digoxigenin (arrows) and visualized using a 590-nm longpass filter. (D) and (F ) same as (C) and (E), respectively, except counterstained with DAPI, excited with UV, and visualized using a 450-nm longpass filter. Arrows point to corresponding Y chromosome-positive cells. (es) Endosteal surface; the actual bone is removed during the denaturing step of the in situ hybridization. Sections are mounted in Vectashield antifade. OM × 746 (A through D); OM × 500 (E and F ).