Detection of male donor cells via XY FISH. Representative XY FISH of frontal cortex biopsy specimen from 4 separate female patients with a history of sex-mismatched stem cell transplantation (A-D) Arrow-head, male donor cells. Light green, autofluorescence background highlighting the tissue architecture. Red probe, Y chromosome; green probe, X chromosome; blue, DAPI nuclei. Original magnification ×400; scale bar, 20μm.