Functional differentiation among the homoeologous chromosomes of common wheat¹⁾

K. TSUNEWAKI

National Institute of Genetics, Misima, Japan

Duplication of genetic materials, followed by functional differentiation of the duplicates due to mutation; is an important genetic process from the viewpoint of evolution. Therefore, it is important to investigate the functional similarity and dissimilarity between homoeologous chromosomes, which have become differentiated from homologues.

Four methods are available for this investigation in common wheat, i.e., nullisomic analysis, monosomic analysis, chromosome substitution method and irradiation of monosomics. The author's results on the functional differentiation of homoeologous chromosomes, hitherto obtained mainly by the second and fourth methods, are summarized and discussed together with those obtained by other researchers.

1. Radiosensitivity of monosomics: There is a differential radiosensitivity between the disomic and the monosomics, the former being more resistant than any line of the latter. A differential radiosensitivity also exists among the monosomics. In homoeologous group 1, mono - I behaved differently from the others, being more resistant to high dosages. All three monosomics of group 2, which is rather sensitive as a group, showed a very f similar pattern of radiosensitivity. In group 3, mono - III was much more sensitive than the other two lines, which were both equally resistant. In group 4, mono - IV was distinctly more sensitive than the other two, mono - VIII being slightly more resistant than mono - XV. In group 5, all three monosomics behaved differently, namely, radioresistance was significantly increased in the order of mono - V, XVIII and IX, the last one being the most resistant among all monosomics. Three monsomics of group 6 showed more or less different patterns but the differences were not significant. All three monosomics of group 7 reacted very similarly to irradiation, all being resistant. These results indicate that all three homoeologous chromosomes belonging to group 2, 6 or 7 have retained almost the same function relating to radiosensitivity, while, in this respect, one chromosome in each of groups 1, 3 and 4 has become differentiated from its two homoeologues, and in group 5 all three homoeologues behave differently from each other.

1) Contribution from the National Institute of Genetics, Japan, No. 423. The work was supported in part by a Grant in Aid from the Scientitic Research Fund of the Ministry of Education, Japan, No. 0431.

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