The karyotypes of 26 species of Vicia were observed and the relationships of the external morphological character and the karyotypes were discussed. For all species, one pair of satellite chromosomes was observed, and in some species of sec. Euvicia a pair of chromosomes with a secondary constriction was also observed. In almost all the species, some submedian chromosomes were observed, while in the others, the chromosomes were subterminal. The total chromosome length and the shape of satellite chromosome were also characteristic in respective species. From this standpoint, the 26 species were arranged in an order taking into consideration the external morphological characteristics and karyotypes.
When male Bombyx mori L. was irradiated with 3kR of gamma-rays as 5-day-old- 5th instar larvae and crossed with unirradiated females, approximately 69% of the fertilized eggs hatched. When F1 males from this treated line were crossed with normal females, the eggs were nearly sterile. Eggs from F1 females showed reduced hatchability. In the F2 generation, fertilities of both males and females were normal, though egg hatchability was somewhat reduced. When males were irradiated as pupae, their progeny inherited less sterility than those from males irradiated as 5th instar larvae. No abnormalities were found in spermatogonial proliferation of F1 males, but chromosome aberrations were frequently observed at meiotic metaphase. The majority of such germ cells became functionless sperms in subsequent spermiogenesis. On the basis of these results, a mechanism for inherited sterility is discussed.
Productivity genes-those affecting fertility or causing full sterility-were analyzed in a cage population of D. melanogaster. Homozygotes for female steriles showed significantly low viability but male sterile homozygotes did not. Positive correlations between male and female productivity were significant in homozygotes but not significant in heterozygotes. Female productivity was not significantly correlated with viability, either in homo- or in heterozygotes. Correlations between male productivity and viability were weakly positive in heterozygotes and significantly positive in homozygotes including or excluding steriles. This suggested that some male productivity genes might be the same genes as those controlling viability. Sterile heterozygotes were generally deleterious but significance was not detected, compared with non-sterile heterozygotes. Female productivity genes showed significant partial dominance in the heterozygotes, while there was no detectable dominance in heterozygotes for male productivity genes.
The changes in frequency of lethal second chromosomes in four experimental populations, which were derived from a successively irradiated population of D. melanogaster with a dose of 5.000R of X rays, were examine. The experimental populations A, B, C and D had been subjected to the accumulative radiation exposures of 10, 000, 25, 000, 50, 000 and 75, 000R, respectively. With the cessation of the irradiation, the frequency of lethal genes decreased in successive generation, being almost equal to or, near the level of original non-irradiated populations. The analysis of the data indicated that the radiation-induced lethal genes with heavy deleterious effect on the fitness of their heterozygous carriers were rapidly eliminated from the population in the early generations after the cessation of the irradiation, and after that the slightly detrimenal lethals were left in the population. The allelism test among lethal genes also showed that the newly induced lethals were evidently deleterious in the heterozygous condition.
Evidence of linkage between the loci of albino gene (i) and color interferer (ci), was given by the data scored on both advanced embryos and adults of hybrids. The two were linked in the repulsion phase, i.e., i, +ci in original albinos and +i, ci in the ci-stock. Two recombinant fish in which one chromosome is linked in the coupling phase (i, ci) were detected out of eleven albino males among F2 of i, +ci/i, +ci×+i, ci/+i, ci. Using these fish as progenitors, ici-homozygotes were bred. Employing appropriate mating types, recombinants (+i, +ci) were observed in three matings of i, ci/i, ci×i, +ci/ +i, ci. The recombination value was found to be 4.6±1.2 percent.