| Mapping of the s and Ch 2 genes on chromosome 3D of
common wheat1) T. KOBA and K. TSUNEWAKI Laboratory of Genetics, Faculty of Agriculture Kyoto University, Kyoto, Japan SEARS (1947) reported that the sphaerococcum gene, s, is located on chromosome 3D, and is ineffective in hemizygous state. One of the two complementary genes, Ch2, for hybrid chlorosis is known to locate on the same chromosome, 3D (TSUNEWAKI and KIHARA 1961). We investigated the genetic distance between the centromere of this chromosome and two genes, s and Ch2, using the ditelo-3DL of Chinese Spring wheat. The results are reported in this paper. For the mapping of the s gene on chromosome 3D, two strains of common wheat were used; those are a ditelocentric line of the long arm of chromosome 3D of a cultivar Chinese Spring (abbreviated to CS ditelo-3DL), supplied by Dr. E.R. SEARS, and an isogenic marker line of a cultivar S615 with the s gene (abbreviated to s-S615) that was introduced from T. sphaerococcum PERC. through ten backcrosses. The breeding procedure taken for mapping this gene is illustrated in Fig. 1. The genotype of the F1 hybrids of the cross, CS ditelo-3DL (SS or - - ) x s-S615 (ss), was assumed to be either Ss or s-. All three F1 plants produced did not show the sphaerococcum character, for its recessiveness in the former case and/or its ineffectivcness in the latter case. Therefore, it could not be determined in the F1 generation whether the s gene locates on the long arm or short arm of the chromosome 3D. The F1 plants were, then, pollinated by s-S615 (ss). In the offspring of this cross, chromosome constitutions and phenotypes (normal vs. sphaerococcum) were investigated with individual plants, the results being summarized in Table 1. If the s locus is on the short arm, it is expected that all individuals which have 42 normal chromosomes should have sphaerococcum character, while all those which have 41 normal plus one telocentric chromosome should exhibit normal phenotype due to the ineffectiveness of the s gene in hemizygous state. In this experiment, however, six recombinants were produced, i.e., five individuals having 41 normal plus one telocentric chromosome and sphaerococcum character, and one having 42 normal chromosomes and normal character. It is, therefore, concluded that the s locus is on the long arm of chromosome 3D, the genetic distance between the locus and the centromere being estimated to be 6/122 or 5.0 + or - 2.0%. |
| 1)The work was supported in part by a Grant-in-Aid (No.048310) from the Ministry of Education. |
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