Mutation of a gene (or genes) for asynapsis and its use in plant breeding¹⁾

M. Okamoto

Shiga Agricultural College, Kusatsu, Shiga-ken, Japan

Compared with the presence of polyvalents at meiosis and consequent low fertility in artificial Aegilops triuncialis (CCC^uC^u), natural Ae. triuncialis is characteristic of regular bivalent formation and high fertility. This regularly bivalent forming characteristics in natural Ae. triuncialis may have been brought about by mutation, chromosome rearrangements, harmony between chromosomes and cytoplasm, and others, (KIHARA and KONDO 1943).

In spite of the very close genetic relationships between homoeologous chromosomes in hexaploid wheats, no chromosome pairing takes place between them. This lack of chromosome pairing was explained by postulating gene mutation which suppresses homoeologous chromosome pairing and by occurrences of repeated inversions (SEARS and OKAMOTO 1956).

The mutational aspects of the above two hypotheses have been very well supported by the finding that a gene (or genes) for asynapsis is located on chromosome V (=5B) of two varieties of common wheat, Chinese Spring and Holdfast (OKAMOTO 1957; SEARS and OKAMOTO 1958; RILEY 1958; RILEY, UNRAU and CHAPMAN 1960).

If the above gene (or genes) for asynapsis has really been due to mutation of a certain gene (or genes) to asynapsis, and not by deficiencies of genes for synapsis, the back mutation of the asynaptic gene (or genes) to synapsis or to the original gene could be expected.

1) This work was done while the writer was supported by a grant from National Science Foundation of U.S.A. to Dr. E. R. Sears at the University of Missouri, U.S.A.

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