By comparison of the standard phenotype, of TM 1 crossed with a testor having recessive markers bw(1) and gl(2), with cytotypes deficient for portions of chromosome 12, genes Bw(1) and Gl(2) were localized in the long arm of 12 between the distal break point 12(8) and the proximal bp 12(11). Recombination values supported a gene arrangement Bw(1) Gl(2) Le(1) N(1) Lf Ne(1) Ms(8). The usage of highly semisterile TN and its associated marker mt demonstrated a significant effect on recombination of adjacent genes and implicated that a chiasmata map for the long arm of 12 is longer than previous estimates. Information about Ms(11) was contradictory possibly because of ambiguous expression of the marker if not its effect on recombination, it being a transgressed gene of G. barbadense with unknown donor DNA contribution.