4. In the 1947 News Letter I mentioned a complex translocation involving chromosomes 3 and 5 in which a break had occurred in 5L midway between the knob and the end, while the centromere of 3 had been fractured. The distal portion of 5L had become translocated to 3S. The linkage relations of genes in chromosome 3 have been determined with respect to the point of translocation, which is the centromere in this case. Due to the fact that directed segregation of the chain of 3 (in strains with two normal chromosomes 5, one normal 3 and the interchanged 3's) may occur with certain modifiers present, it was not feasible to use pollen abortion as the marker for the translocation, and root-tip counts were resorted to. Plants with 20 chromosomes had the intact chromosome 3 while those with 21 chromosomes had 3S and 3L as separate entities. The following data were obtained:




% recombination





(C represents the centromere)














Anderson and Randolph state that the centromere lies between d1 and

ts4. The data obtained in the study of this translocation permit a more definite location and show that the centromere lies between d1 and Rg, with Rg lying between ts4 and the centromere. The linkage map is shown below (C standing for the centromere):


cr      d    C      Rg ts4       ba      na     A      et      ga7

0       18   25     40 47       .64      75     103    115     121


M. M. Rhoades