Recent work with starch gel electrophoresis of coleoptile extracts has indicated that Hexl, the structural locus for the most anodal set of hexokinase isozymes, and Tpi4, which encodes the slowest migrating set of triose phosphate isomerase bands, are located on chromosome 3. Their placement relative to previously mapped isozyme loci on this chromosome (E8, Pgd2, Got1, Me1, and Mdh3 - see Goodman and Stuber, 1983, In: Isozymes in plant genetics and breeding, Part B. S. D. Tanksley and T. J. Orton, Eds., Elsevier) was revealed through the analysis of an F2 between the two inbreds CM37 (E8-4.5, Hex1-null, Tpi4-4, Pgd2-5, Mdh3-16) and T232 (E84, Hex1-4, Tpi4 -null, Pgd2-2.8, Mdh3-18). Joint segregation data and maximum likelihood estimates of recombination fractions are presented in Table 1.
These data are consistent with the previously reported relationships among the loci E8, Pgd2, and Mdh3, and further indicate that Hex1 and Tpi4 lie between E8 and Pgd2. The placement of Hex1 on the short arm of chromosome 3 was confirmed with a cross of the B-A translocation stock TB-3Sb (Hex1-4) onto our Hex1-null tester (Ky201). Null phenotypes (i.e., hypoploids) were recovered in 5 of 13 plants examined. These data collectively lead to the following isozyme map for chromosome 3:
The discovery of the markers between E8 and Pgd2 forces the genetic map to grow by about 12 units (E8-Pgd2 = 24 + 17 + 10 = 51 vs. older reports of 39, see ref. above).
J. F. Wendel, C. W. Stuber, and M. M. Goodman
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