AB chromosome translocation analyses place on short arm of chromosome 4 (4S; Simcox and Weber 1985 ). There is close linkage to other genes in the benzoxazinoid synthesis pathway [bx2, bx3, bx4, bx5 Frey et al. 1995, 1997 ). Gene bx1 is 2490 bp from bx2 (Frey et al. 1997 ); between umc123 and agrc94 on 4S (Melanson et al. 1997 ). Mapping probes: SSR p-umc1022 (Sharopova et al. 2002 ); Overgo (physical map probe) PCO06449 (Gardiner et al. 2004 ).