Chiasmata-like structures are increased in Blm CKO cells. (A) Diakinesis spreads from Blm^cko/neo mice, shown by abnormal numbers of COs on single chromosomes (arrows) and structures between chromosomes (arrowhead). The mean values of chiasmata per cell counted from Blm^flox/neo and Blm^cko/neo mice showed a significant difference (*, P = 0.0035 by Welch’s t test). (B) The number of chiasmata per individual chromosome pair was significantly different between the CKO and control (C) mice (**, P = 0.0053).