XY FISH signals in pachytene. FISH on prophase I chromosomes from the exfoliated spermatocytes found in the ejaculate of an azoospermic carrier of dic(9;13)(p11.2;p12). A. Example of an association of chromosomes involved in the dic(9;13)(p11.2;p12) translocation with an XY bivalent and additional chromosomes 5 and 22 (MultiFISH signals, false colours) (MetaSystems). B. Bi-colour FISH signals with paint probes showing the XY bivalent in meiotic pachytene (red probe = X chromosome; green = chromosome) (the FISH probes are described in Additional file 1: Table S1).