抄録
1) The original fatuoids used in this work were supplied by Dr. C. L. HUSKINS, who had already studied them.
2) Heterozygous fatuoids from three strains, H58, H20 and H93 segregated in the following generation normals, hetero- and homozygous fatuoids in a 1:2:1 ratio. The genetic results confirmed practically HUSKINS' observations.
3) Many segregates from each phenotype were cytologically studied. In all of them except 4, normal 21 bivalents were generally counted at the heterotypic metaphase in PMC. On the other hand, uni- tri- and tetravalent chromosomes were observed in a few PMC from some of these plants. The statistical counts of their occurrence are shown in Tables 2-4. From these results we can see that meiotic abnormalities occur independently of the phenotypic character of the grain, and appear to be not directly transmitted from generation to generation. The chromosome irregularities may be caused mainly by the lack of cytological equilibrium and by the polyploidy in Avena.
4) There were found to be 5 segregates with 41 chromosomes that arose in each of the phenotypes. They were probably produced through meiotic irregularities in the parent plants.
5) From them 2 heterozygous fatuoids, H58-12 and H20-35, segregated dwarf homozygous fatuoids, heterozygotes and normals in a ratio of ca. 1:1.5:0.1. The progenies from H58-12 were extensively studied. The dwarf homozygous fatuoids had 40 somatic chromosomes, but the formation of bivalents was much reduced, 0-10II, being counted so far observed. Therefore they were completely sterile. A few of low fertile homozygous fatuoids were found. Their chromosome combination might be 20II+fc1I Heterozygous fatuoids had 20II+1I. Their fertility varied widely, probably owing to the external conditions (Tables 7 and 8). Normal segregates appeared to be quite normal in the cytological and morphological features as well as in fertility. The abnormal segregation ratio is discussed with special reference to the cytological behavior.
6) The 3 other plants with 41 chromosomes lacked different chromosomes, which do not bear factors for the fatuoid and cultivated type of the grain characters.
7) Three main hypotheses on the origin of fatuoids are discussed from the genetic and cytological points of view.
8) Basing on the genetic and cytological behavior fatuoids are classified into two main groups. The first series contains fatuoids produced by the mutation of a gene complex in the c-chromosome. The common fatuoid belongs to this class. Fatuoids of the second series arose through chromosome aberrations. Owing to the deficiency of a whole chromosome the meiotic and genetic features are very abnormal.
