• Yoshitaka Imai

      Articles written in Journal of Genetics

    • The types of spotting in mice and their genetic behaviour

      Masao Sô Yoshitaka Imai

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      The results reported in this paper agree in the main with those of Little and Detlefsen. More experimental evidence, however, is supplied by the present investigation.

      In the present studies, however, the dominant spotting of the “Kasuri” race was distinguished and separately recorded from the recessive ordinary spotting, so the comparison between observation and expectation was more closely dealt with.

      The D factor acting upon S, the factor for self, in somewhat restricted fashion on the development of the coat-colour results in the “Kasuri” pattern, and the same factor working upon S’, a factor for the spotting, results in a dark-eyed white of the “Daruma” type.

      On the one hand the D factor acts as dominant upon the pattern development as was stated above, and on the other hand it works recessively in regard to the lethal effect. Mice homozygous for this factor perish in the early ontogeny whether they have S or S’ as the hypostatic factors.

      The “Kasuri” race often become sterile, especially on the female side. This condition was also found to occur in the “Daruma” race in a few instances.

    • Genetic behaviour of the willow leaf in the Japanese morning glory

      Yoshitaka Imai

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    • A genetic study of green-variegated yellow leaves in the Japanese morning glory

      Yoshitaka Imai

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    • Experiments with a pear-leafed and fasciated strain of the Japanese morning glory

      Yoshitaka Imai

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    • Studies on yellow-inconstant, a mutating character ofPharbitis Nil

      Yoshitaka Imai

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    • Analysis of flower colour inPharbitis Nil

      Yoshitaka Imai

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    • An apparently simple inheritance of variegation inPolygonum orientale

      Yoshitaka Imai

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      The variegated form ofPolygonum orientale L. is outwardly simple recessive to self-green in inheritance, but its white patches and branchlets are products of the exo-mutations of green plastids, which are mutating frequently to white owing to the action of a recessive stimulating gene carried by the stock. The albinotic seedlings, which might be expected from the achenes of the variegated plants as well as those collected on the white branches, are not obtainable, because the fruits do not germinate. This fact eliminates the possible production of albinotic seedlings, and simplifies the segregation of the variegated form in its inheritance.

      This plant seems to be a di-histogenic dicotyledon, whose general plant body is possibly derived from two histogens, while its stipules are from the outer histogen only.

      I am of the opinion that, in view of the foregoing remarks concerningPolygonum, some cases of other plants that have been reported as being Mendelian in inheritance, should be checked by experiments.

    • Variegated flowers and their derivatives by bud variation

      Yoshitaka Imai

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      The anthocyanin variegation due to mutable genes gives bud variation in accordance with a definite mechanism of ontogeny. In the variegated azaleas, bud variations occur in various directions, including those to the ground colour. These sports can be explained by recurrent mutation, and sometimes by somatic rearrangement of tissues. The fringed flowers ofRhododendron, Punica, Chaenomeles, andCamellia are regarded as periclinals with mutated, self-coloured meso-histogens. In certain other plants however fringing does not appear in similar periclinals, owing to differences in the extent of development of the ecto-histogen in corolla ontogeny. Sometimes the mutated or the genotypically different mesohistogen does not affect the flower colour or coloration, because the tissues do not contain any pigment.

    • The structure ofAlbomargin ata andMedioalbinata forms

      Yoshitaka Imai

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      From both experiment and theory, our knowledge of the structure of thepseudo-medioalbinata, albomarginata, andmedioalbinata leaves may be summarised as follows:

      Thepseudo-medioalbinata form is a green-over-white periclinal, modified secondarily by the influence of the albinotic endohistogen. Its progeny therefore are all green. Root cuttings may give rise to albinotic shoots.

      Thealbomarginata form is a periclinal with white ectohistogen in dihistogenic plants. In these plants, the ectohistogen develops into the epidermis and the marginal mesophyll of leaves, while the endohistogen constitutes the other inner components. The white-fringed leaves of such trihistogenic dicotyledons asDaphne andFragaria are due to the development of the white ectohistogen that forms the epidermis and the fringed mesophyll of the leaves.

      Themedioalbinata form, which occurs in some monocotyledons, is due to the green-over-white arrangement of the two histogens.

    • Geno- and plasmotypes of variegated pelargoniums

      Yoshitaka Imai

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      Variegated and periclinal pelargoniums offer some very puzzling problems. Chittenden (1927) collected some of these cases, which, however, have become simplified as the result of my investigations. Two forms of variegation were identified, the one due to sorting out of mixed plastids, and the other to recurrent exomutation of plastids induced by a recessive stimulant gene that is mutable itself. Various plasmotypes of plastids differ in their colour, the degree of crumpling of tissues, and mutability. The plasmotypic change of plastids is either automutable or exomutable, while sometimes the plastids transform in two directions. The white-over-green periclinals generally have albinotic epidermis. In the majority of cases unstable chlorophyll periclinal types change into stable types, probably at the growing points. Freak of Nature, Chittenden’s variety A, and the green crêpe sport from Hanamikado are periclinals with differentiated ectohistogens, it being green in the first named and albinotic in others. The extent to which the respective three histogens contribute to the ontogeny of the plant body is considered from both anatomical and genetic investigations. Since in leaf formation of the pelargonium the ectohistogen develops into the marginal mesophyll as well as the epidermis, the mesohistogen into the outer and submarginal mesophyll, and the endohistogen into the innermost mesophyll, the chlorophyll periclinals with differentiated ectohistogens bear leaves with margins of a different colour.

    • The mechanism of variegation inPlantago andCapsicum

      Yoshitaka Imai

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      The variegations seen inPlantago andCapsicum behave as recessives to normal green, but their true genetic nature is complicated. The white patches in the variegated leaves have green ticks. The mechanism involved in variegation consists in white patches resulting through exomutation of the green plastogene, and in green ticks by automutation of the white mutant plastogene. Almost white sports and white-over-green periclinal sports appear. In the course of sexual reproduction, retroversion to the apparently green condition takes place, so that white and periclinal branches or ears generally produce variegated seedlings.

    • Variation in the flaked lines ofLathyrus odoratus

      Yoshitaka Imai Yasuo Hnuma

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      1. According to Punnett, the constitution of our flaked sweet pea seems to beG1G1d3d3. In the flaked America the offspring consisted of 3·54% self-coloured, 2·93% dark-flaked, 93·22% flaked, and 0·32% tinged, showing the rate of inconstancy to be high.

      2. The inconstancy of the flaked is attributed to the following recurrent gene mutations:$$\begin{gathered} G_1 \leftarrow G_1 \prime \to g_1 \prime \hfill \\ d_3 \leftrightarrows D_3 \hfill \\ \end{gathered} $$

      The self-coloured is due to the change fromG1′ toG1, the dark-flaked to that fromd3 toD3, and the tinged to that fromG1′ tog1′.

      3. Punnett’s hypothesis agrees well in the matter of genotypes of the mutant forms that appeared in our culture. His material was derived from Senator, which is a flaked line with high constancy. Our flaked America and Felix, however, showed marked inconstancy in the related genes. Somatic variation with genic changes also occurred.

    • Sex-linked mutant characters in the hemp,Cannabis sativa

      Yoshitaka Imai

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    • Recurrent mutation in the flaked alleles ofPharbitis purpurea

      Yoshitaka Imai Kiyoo Tabuchi

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