Effect of disruption of Cds1, Chk1, Mek1, and combinations of these checkpoint kinase mutations on DSB formation. pat1-114 (WT) or pat1-114 hsk1-89 cells in combination with checkpoint mutations indicated were induced into meiosis, and DSB formation was analyzed by pulsed-field gel electrophoresis. The brackets indicate the positions of the meiotic breaks. Chr 1, Chr 2, and Chr 3 indicate the positions of chromosomes 1, 2, and 3, respectively.