Ag. tsukushiense var. transiens, a weed growing in fields and along road-sides, is a very common hexaploid species (2n=42), widely distributed in Japan, China, Manchuria and Korea. In a valley of the hilly neighborhood of Misima, a spontaneous polyhaploid plant (2n=21) of the species was found. It was smaller than the hexaploid strains, but its tillering was very vigorous. In natural condition it yielded two seeds which were assumed to have been produced by pollination with the pollen of hexaploid plants growing in its proximity. The two seeds gave two plants, one a monosomic (2n=41) and the other a disomic (2n=42). Pollen fertility of the polyhaploid, the monosomic and the disomic was 0.001, 28.5 and 78.5%, and seed fertility was 0, 53.3 and 76.6%, respectively. The polyhaploid was crossed by the disomic and by two hexaploid strains, and the crossing success amounted to 0.7-1.6%. As to chromosome pairing at MI of PMCs, the polyhaploid showed 21I in 84% and 1II+19I in 14% of 442 cells observed. In the majority of cells chromosome pairing in the monosomic was 20II+1I. From the result it is concluded that Ag. tsukushiense var. transiens is an allohexaploid whose genome constitution comprises three different genomes. Summarizing the cytological studies of polyhaploids in Agropyron, the types of polyploidy in this genus are assumed to be various and complex.
In D. melanogaster, there can be detected at least seven amylase bands (isozymes) on agar-gel zymograms. They are called Nos. 1-7 from the anode side (Figure 1). Amylase patterns are specific according to strains. For example, the Amy1 strain shows only one strong amylase band No. 1, whereas the Amy2.6 strain shows two strong bands, Nos. 2 and 6. At present, seven strains with different amylase patterns have been established. Amylase patterns of these strains are always controlled by a gene or genes linked very closely at locus 78 on the second chromosome. They are probably allelic and co-dominant with one another. The F1 individuals between any two strains with different amylase patterns, show only mixed bands of the parental patterns, that is, no hybrid band has been detected on the zymogram. Studies on amylase isozymes may contribute not only to the problem of population genetics of D. melanogaster, but also to the evolutionary history of the genus Drosophila.
Eight cases of schizophrenia were studied with respect to their chromosome constitutions, based on short-term cultures of leucocytes from peripheral blood. All cases showed no visible change or detectable variation from a normal chromosome complement.
Flies of a new mutant with wings transformed into halter-like or other shaped appendages were found by T. Kanehisa in the wild strain of Drosophila virilis collected at Sapporo (Hokkaido, Japan). Phenotypical changes are observed also on the thorax and the scutellum. As the mutation phenotypically resembles the “tetralteraBd” of Drosophila melanogaster reported by R. B. Goldschmidt, we named the mutation “tetraltera” (tet). Flies homozygous for tet show a penetrance of about 10 percent, whereas about 0.2 percent of flies heterozygous for the mutation show the mutant phenotype. It is determined that the tet gene is situated on the fourth chromosome, but the locus is not yet definitely determined. Another mutation which looked like tet was found in the Notch3a stock of D. virilis. This mutant strain has a low penetrance of about 0.07 percent and flies heterozygous for the gene phenotypically show the wild-type. The gene of this mutation is supposed to belong to the second linkage group, though there is some uncertainty about this because of its extremely low penetrance.
The reductoisomerase in the biosynthetic pathway leading to isoleucine and valine is represed by L-valine, but not by isoleucine in Escherichia coli K-12. The mode of repression in a methionine-requiring mutant is different from that of wild type. The reductoisomerase of the methionine-requiring mutant and its derivatives, the isoleucine-valine requiring mutants, is repressed by valine to a low level, if the molar ratio of L-isoleucine to L-valine in the medium is below 1. On the other hand, the synthesis of the reductoisomerase in the wild-type strain is gradually decreased by increasing amounts of L-valine in media containing a constant amount of L-isoleucine. The repression by L-valine is specific for the reductoisomerase and independent of the induction of β-galactosidase.
The present paper deals with some observations on X-irradiated early mouse embryos at different stages after fertilization, with special regard to the incidence of abnormalities. The mice used were F1 hybrids between inbred strains, dd/Mk and CBA/Mk, aged nearly 80 days. Virgin females were mated by being placed with males at the ratio of 1_??_:1_??_ during a period from 6.00 p.m. to 9.00 a.m. of the next morning. The females with plugs were irradiated at the two different stages after fertilization; a) 12 a.m. on the 1st day after mating (0.5 day embryo); and b) 12 a.m. on the 2nd day after mating (1.5 day embryo). X-rayirradiations were 5r, 15r, and 25r in dose. The results obtained are summarized as follows: 1) the number of resorbed foetuses increased in 0.5 day embryos than that of 1.5 day embryos; 2) the rate of resorbed foetuses was influenced by dosages, but the rate of dead foetuses did not remarkably differ by dosages; 3) a few incidences of exencephalia and polydactylia of the hind foot were obtained in experimental groups; 4) abnormal foetuses with polydactylous condition on the fore foot were observed in both control and experimental groups, being strickingly high in the irradiated groups; and 5) histological observations revealed that the cartilaginous ossification occurred in the polydactylous foot. It was concluded that the low level irradiation of X-rays affects the very early mouse embryo.
The tulip flower develops inside the bulb during storage, and the color spots appearing on the perianth were induced by gamma-irradiation. If irradiation was carried out in the critical period shortly before the completion of perianth formation, the color spots appeared at random in single or a few epithelial cells. As previously reported, the extent of mutation was reduced at low intensity as compared with high intensity exposure. Therofore, the spots are considered to be due to somatic mutation of epithelial cell being caused by chromosomal deletion through irradiation. In the present paper, in order to elucidate the nature of the genetic change, i, e., whether genic or chromosomal, quantitative studies of total dose, fractionation and temperature effects on the somatic mutation have been studied. The results are summarized as follows: 1) The data refer to the number of mutant cells per unit area. Therefore, growth inhibition of the perianth was undesirable. But measurements of the size of perianth showed very rarely inhibition after irradiation by 200r in total dose in October. 2) Cell division of the epithelium at the time of irradiation, in October and November, was estimated from the average number of mutant cells per spot, which was 1.13 and 1.02 at 200r, respectively. These figures indicate that the epithelial cells of the perianth may not undergo division after November. 3) Frequency of color spot occurrence after single acute exposure was examined at doses of 25 to 200r at 600r/h. The dose response curve is rather exponential. 4) A total dose of 100 or 200r was fractionated into 2 or 4 doses of 50r and 100r, respectively, and with intervals of 30 to 1440 minutes and the effects were compared with that of single dose. No reduction of mutation was observed when the interval lasted 30 minutes, while in the case of fractionation into 4 doses at the same interval, the number of mutations was reduced as compared with a single dose. When the interval lasted 1440 minutes at the total dose of 100r and 200r, the number of mutation was markedly reduced to that obtained at non-fractionated dose. 5) The number of mutations increased at low temperature (-2° to 2°C) during irradiation as compared with that obtained at 12.5°C. These results show that chromosome reunion after deletion may be involved in the color spot formation induced by gamma-rays.