Several zebrafish mutants with defects in meiotic processes develop solely as males, including those with mutations in chromosome axis genes sycp2 [70] and sycp3 [74], the meiosis-specific cohesin subunits smc1b (ortholog of human SMC1β) [116] and rad21l1 (ortholog of human RAD21L) [71], and the DSB repair genes brca2 [69,72], rad51 [117] and fancl [68] and other Fanconi anemia genes [58] exhibiting a range of phenotypes from shortened axial structures, reduced DSB formation, unrepaired DSBs, and asynapsis. This evidence concerns the gene SMC1B and Fanconi anemia.