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XY chromosome pairing as studied by X (green) and Y (red) chromosome painting in tissue sections. (A) Stage VI tubule of a Ku70−/−Rap1Δ/Δ testis showing pairing (touching) of XY signals in pachytene spermatocytes (arrow). (B) Stage XII tubule of a double knockout testis showing XY bivalents with close signal apposition in metaphase I plates. Blue, DNA stain DAPI. Signal distribution in wild type and heterozygotes was essentially the same (not shown). Scale bars: 10 µm.
