Relative fitness of the genotypes at the B locus determining blood groups in chickens was studied in two closed lines and their cross-breds. These lines, which were derived from one population and have been closed more than ten generations, were maintained by reciprocal recurrent selection at the Takikawa Livestock Breeding Station. Both lines possessed five alleles at the B locus, respectively. However, in one line one of them was extinct in 1959.
Comparisons among the expected total, observed total and selected frequencies of the genes and the genotypes were performed for each generation. There was no obvious tendency in gene frequencies. On the other hand, the comparisons of geno-typic frequencies revealed apparent selective advantage of heterozygotes. The observed frequency of heterozygous genotypes in each total population was higher than the expected frequency. The proportion of heterozygotes increased again after selection. Thus, both natural and artificial selections favored the heterozygotes at the B locus. These results suggest that the B blood group in chickens is an example of balanced polymorphism.
Direct comparisons of the characters under selection between the genotypes at the B locus showed, however, that the superiority of heterozygotes was not explicable by any single character studied here.

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By using subcritical temperature and ultraviolet light as DNA-attacking agents, the duplex nature of gene mutation of ad locus in yeast cells has been studied at molecular level.
The relative frequencies of whole-colony mutation and fractional-colony (sectored) mutation induced by these two agents are strikingly different: 59% whole, 23% fractional and 18% undefined for subcritical temperature; 14% whole, 72% fractional and 13% undefined for ultraviolet light. The results are interpreted to indicate a genetic multiplicity of two of the gene, based on the assumption that subcritical temperature causes changes in both strands of a gene-DNA molecule and ultraviolet in one of the two strands by a single event.

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Torenia fournieri Lind. (2n=18) is known to occur in three flower colors, deep blue-purple, pale blue-purple and white. The pale blue-purple form was found in a population of the deep blue-purple form. The deep blue-purple and pale blue-purple flowers and those of six F₁ hybrids among the three forms were determined to contain the same three anthocyanins, namely, malvidin-, petunidin- and delphinidin-glycosides. The white flowers were also found to contain traces of the anthocyanins. Malvidin-glycoside is the major component in all forms; it was isolated in crystalline form and identified with malvin. The other two are minor components.
It was concluded from F₂ segregation that the genotypes of the three forms were AABB, AAbb and aaBB for deep blue-purple, pale blue-purple and white respectively, and that A and B are basic complementary genes controlling anthocyanin formation. The double recessive genotype aabb may be ascribed to the completely acyanic segregant with pure white flowers. Further, the effects of genes A and B on anthocyanin formation were estimated for six different genotypes.
Thus the concentrations of the anthocyanins show the following relations;
AABB=AaBB>AABb>AaBb>AAbb>aaBB>aabb=0
It was found that dominance of A over a is complete and that of B is incomplete under the present environmental conditions.

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1) Salivary gland chromosomes of Drosophila nigromaculata obtained from natural populations in Hokkaido has revealed a remarkable chromosomal polymorphism. Twenty-two different inversions were found in heterozygous condition in 57 samples, in total 101 inversions being recorded; 26.3 in percentage. The inversions were found in the X, A, B, C, and D arms, while the dot-like E arm showed no aberration in samples so far studied.
2) The frequency of inversions in each chromosome was as follows; 9.11% for C, 6.77% for D, 6.51% for A, 2.34% for B and 1.56% for X.
3) A possible meaning in adaptation of non-random association of inversions was suggested.

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1. Artificial populations containing reciprocal arrangements, A and B, of the third chromosome due to a terminal inversion, In3L, of Drosophila ananassae were studied. All populations reached equilibria at about 60% A and 40% B after 3-4 months.
2. Heterosis regarding the karyotypes, AA, BB and AB, was expressed in longevity, viability, hatchability, fecundity and rate of development.
3. AA was always superior to BB in longevity, viability and rate of development.
4. Some differences between AB and BA heterozygotes raised by reciprocal crosses were observed in fecundity, longevity and rate of development in poor medium with only 5% boiled yeast.
5. Comparing net adaptive values estimated by measuring life cycle components with those from population cage experiments, a close coincidence was ascertained for AB as well as for AA, although an underestimation was found for BB homozygote.

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The frequencies of haploids in nucleus-substitution lines of T. vulgare var. erythrospermum and Taylor's Triticale having the cytoplasm of Aegilops caudata, were investigated and compared with those found in the ordinary strains.
The haploid frequency of the former was 1.7%, while it amounted to 53% in the latter. No haploids were found in the respective controls. The differences are significant in both cases.
This result indicates that an alien cytoplasm will increase the tendency of a species to develop parthenogenetically haploid embryos. The difference between T. vulgare var. erythrospermum and Taylor's Triticale indicates that different genotypes respond differently to the same alien cytoplasm.
The use of an alien cytoplasm provides a new means for artificial production of haploids.

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The sterility of F₁ hybrids between cultivated rice varieties (Oryza sativa L.) has been regarded as an index of phylogenetic relationships. In this study an extensive survey was made of the sterility relationships in Asian wild rice, O. perennis Moench, which could be the progenitor of cultivated rice. It was found that the wild strains were mostly inter-fertile and gave fertile F₁ hybrids with sativa varieties which were partly inter-sterile. The data for F₁ pollen fertility obtained with five test-strains were studied by using the technique of principal component analysis, together with similar data for sativa strains previously obtained by the second writer. The results showed that the Asian wild-rice forms have a potentiality to differentiation into Indica and Japonica types, and that differentiation might advance with the approach to the cultivated type. Further observations were made regarding intra-populational variations in sterility factors. The sterility frequently found in the populations of perennis type was considered to be due to genetic factors with diplontic or zygotic effect, possibly of the same kind as the duplicate-fertility genes (Oka and Doida 1962). In addition to this, the populations were found to contain factors responsible for the gametic sterility of F₁ hybrids, which Oka (1957a) called gametic-development genes. It was inferred that wild rice carries double-dominant combinations of those duplicate genes, so that it produces fertile F₁ hybrids with sativa varieties of different types, which might have become inter-sterile after recessive mutations or deficiencies had taken place at one or the other of those loci. Variations of those genes within populations indicate the potentiality of wild rice to form partly inter-sterile groups.

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This study was attempted with the view to looking into the evolutionary dynamics of ultivated rice. A review of previous theoretical studies on partly self-pollinated plant populations was set out first. Then, the writers' computations were reported which dealt with the effects of seed dormancy and vegetative propagation on population structure, and the change in frequency of a gene controlling selfing probability. It was pointed out that the breeding system of the Perennis type of wild rice, which is partly cross-pollinated and capable of propagating vegetatively, and has seeds dormant for a long period, would be quite suitable for accumulating genetic variation in its populations. It was also suggested that selfing genes can increase by themselves unless counteracted by another force favoring heterozygotes. Therefore, if the habitat assumes conditions of cultivated fields and homozygous plants become relatively advantageous, the populations will tend toward selfing.

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The reduction division in PMC's was studied in 5 interspecific hybrids: N. knightiana ×N. rustica, N. repanda×N. palmeri, N. trigonophylla×N. palmeri, N. bigelovii×N. megalosiphon, and N. debneyi×N. otophora.

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At first ana-telophase and second ana-telophase in the PMC's of Trillium kamtschaticum Pall. which were irradiated with X-rays at various stages from diplotene (presumed) to first metaphase, the diagnostic configurations of half-chromatid recombination, viz., 2-side-arm bridges were frequently observed. So far as the PMC's irradiated at stages from mid-prophase to first metaphase are concerned, the earlier is the meiotic stage of the cells, the lower is the frequency of 2-side-arm bridges resulted.
Almost all of 2-side-arm bridges are supposed to be brought about from exchange or union between two non-sister half-chromatids of two associated chromatids, whose possibility is suggested from spatial relationship of the four chromatid threads in a bivalent at late prophase and first metaphase.
The present findings indicating that the occurrence of 2-side-arm bridges is so frequent regardless of the number and position of interstitial chiasmata may well be explained on the basis of Matsuura's Neo-two plane theory, that is, free two-by-two disjunction of the four sister kinetochores of a bivalent at anaphase after free opening-out of the chromatids at diplotene.

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