Y-chromosome in situ hybridization in brain sections. (A through C) male brain sections; (D through F ) female brain sections; (G through I) transplanted female brain sections. The total number of donor cells in the brain was estimated by counting individual male cells in 1 of every 25 sagittal sections from half of the brain and then multiplying this number by 50 (see Materials and Methods for details). The arrows indicate a single male cell found in one representative section from a female transplant recipient. (A, D, and G) Show the fluorescein-labeled hybridization signal; (B, E, and H) show counterstaining with propidium iodide, and (C, F, and I) show combined images. Magnification = 1,000× for (A) through (F ), and 1,200× for (G) through (I).