Two-color FISH was carried out as described , with small modifications. Briefly, chromosome preparations were denatured in 70% formamide/2x saline-sodium citrate (SSC) solution for 5 min at 75 °C, and dehydrated in standard series of precooled ethanol at −20 °C; the DNA probes in hybridization mixture were denatured separately for 5 min at 95 °C; then hybridization was carried out overnight in a humid chamber at 37 °C. After hybridization, slides were washed under low stringency conditions (3 times for 5 min each, in 50% formamide/2xSSC at 45 °C, 2xSSC at 45 °C and 0.2xSSC at 45 °C). Counterstaining was done by Vectashield Antifade Mounting Medium (Vector Laboratories, Burlingame, CA, USA) containing 4′,6-diamidino-2-phenylindole (DAPI) (Vector Laboratories) applied directly under a coverslip that was then sealed with rubber cement.