| II. SUPPLEMENT Wheat and its Relatives1) H. KIHARA and K. YAMASHITA National Institute of Genetics, Misima, Japan and Biological Laboratory, Kyoto University, Kyoto, Japan Classification of Triticum In 1913 Schulz divided wheat specics into three main groups, Einkorn, Emmer and Dinkel, from the morphological view point. In 1918, Sakamura and Sax found the right chromosome number for each group as n=7,14 and 21, respectively. Following this finding, Kihara accomplished the genome constitution for each group as AA, AABB and AABBDD, respectively. Timopheevi (n=14) was afterwards separated from Emmer group by the genome constitution AAGG. "Genome which is represented by a chromosome set is a fundamental genetical and physiological system, whose completeness as to the basic gene content is indispensable for the normal development of gones in haplo- and zygotes in diplophase." Pentaploid Hybrids The investigation of pentaploid hybrids (Kihara 1919, 1924) gave an early start to Kihara's genome-analysis. The pentaploid hybrids were won from crosses between Emmer and Dinkel wheats. Consequently, their genome constitution is represented by the formula AABBD. Kihara (1924) found the pentaploid hybrids to follow definite rulcs which he derived from the chromosome combinations in F2. On their basis he divided the F2 offspring into two groups: 1) "fertile" and 2) "sterile" chromosome combinations. The first group was further subdivided into a) the chromosome number decreasing group and b) the chromosome number increasing group. The first has 28-34 somatic chromosomes and at metaphase the configuraion 14II (7AA+7BB)+(0I-6I from genome D). The 29-34 chromosome plants revert soon in the course of further generations to the Emmer type with 14II, i.e. AABB, when all the univalents of the incomplete genome D have dropped out. The increasing group, with 36-42 somatic chromosomes, consists of plants which possess all elements of D, double or single. This group, when bred further, reverts slowly to the 42 chromosome type, AABBDD, by acquiring in the process of fertilization the missing partner of the D complement. Thus, in further generations of the pentaploid hybrids and, in general, all hybrids of the genome pattern AAB return parental genome types, where cytological and eventually, genetical constancy is established. The "sterile" chromosome combinations can never revert to the parental types and, with a few exceptions, die out. Results of the "Aequationskreuzungen," i.e. F1 x parents, and "Zertationskreuzungen," i.e. parents x F1: The purpose of the first series was to explore the distribution of the various chromosome combinations in the macrosporocytes of the hybrid and to ascertain the fitness of the corresponding gametes. The object of the second series was to examine these conditions for the microsporocytes. The obtained ratios were not in good accord with the theoretical figures, calculated on the basis of a random distribution of univalents. The search began for the causes of the disagreement. The first clue gave the fast development of the decreasing group back to AABB from which an elimination of univalents could be inferred, and calculations have been worked out to determine the degree of elimination. The followings should be mentioned. |
| 1) Excerption with necessary revisions and corrections from EXHIBITS, International Genetics Symposia, 1956, 6-12 September, Tokyo and Kyoto, Science Council of Japan, 1956 |
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