Mutation Arrest point Synapsis phenotype Reference A-myb Early pachytene Not reported Toscani et al., 1997 Atm Zygotene/early pachytene Frequent asynapsis Xu et al., 1996 Dmc1 Zygotene/early pachytene Asynapsis Yoshida et al., 1998 Msh4 Zygotene Frequent asynapsis; Nonhomologous pairing Kneitz et al., 2000 Msh5 Zygotene/early pachytene Frequent asynapsis; Nonhomologous pairing Edelmann et al., 1999 Scp3 Zygotene Asynapsis Yuan et al., 2000 Spo11 Zygotene Asynapsis Baudat et al., 2000; Romanienko and Camerini-Otero, 2000 XSxr(a)0 Late prophase/meiosis I Asynapsis of the sex chromosome Odorisio et al., 1998 Hsp70.2 Late pachytene Failure to desynapse Dix et al., 1997 Mlh1 Late pachytene Failure to desynapse Edelmann et al., 1996 Cyclin A1 Late pachytene/diplotene Incomplete desynapsis D. Liu et al., 1998