注記 |
In this paper, the authors described the hereditary behaviors of the Toyama's grey egg (Toyama, 1912, 1913) and the collapsing egg (Sado, 1957), phase-contrast microscopic observations of the surfaces and cross-sections of these abnormal egg shells, and the comparative examination of the separation of the components both of the collapsing and the normal eggs by centrifugation. Then some problems were discussed about the genic actions of these two and other grey egg genes and the complex nature of the Gr multiple allelic locus. 1. Toyama's grey egg in the silkworm. e6 stock in our laboratory, manifests phenotypically following characteristics ; the shell of which is opaque and milky white in color, the egg looking grey due to optical combination with the dark serosa pigments, the surface of the shell is not smooth but become irregularly corrugated when the ventral plate is formed, there is no depression in the egg surface and further, as to the shape, it shows slightly spindle form (Plate 21-1). Genetically, however, these characters are controlled by a single dominant gene, Gr (Tanaka, 1943). Gr heterozygous female moth deposits grey eggs, while Gr homozygous one B-grey eggs which are phenotypically significantly different from the grey eggs, and the shells of which are thin and translucent, manifesting normal dark egg colors, but as to the shape,they resemble to those of grey egg (Plate 21. 3). Accordingly, in order to obtain moths depositting grey eggs we have only to cross normal egged breed with B-grey one. Recombination values between p, Gr and Y genes calculated after three points experiments were p-Gr=6.5, Gr-Y=18.9 and p-Y=25.4, which coincide with those of Tanaka (1943). 2. Collapsing egg was for the first time found by the senior author (1957) as a spontaneous mutation in the p22 stock (Normal egged breed; Japanese race, Yamato-Nishiki). It shows evidently spindle shape immediately after deposition, but in about half an hour after oviposition it becomes completely depressed to the bottom (Plate 21. 6-7). This character is completely recessive to the normal egg, and is controlled by a single recessive collapsing egg gene, symbolized as Gr^col Recombination values between p-Grc°t-Y loci after three points tests are p-Gr^col=5.3, Gr^col-Y=21.5 and p-Y=26.4, respectively. As in the chromosome map of the silkworm so far established map distance between p and Y loci is 25.6 units, we must correct the values described above, and get p-Gr^col=5.1. This coincides with the Gr-16 locus determined by Takasaki (1947). 3. Gr/Gr^col female moth produces new type variant eggs, owing to the interaction between Gr and Gr^col genes. This variant egg shows phenotypically intermediate between Gr/Gr and Gr/+, that is, the shell of which is partially translucent and the surrounding part of it shows milky white color, and the shape of which resembles to those of B-grey or grey eggs. 4. In order to test the pseudoallelic relation between Gr and Gr^col genes, the authors tested the Gr/Gr^col sib-mating with p^3- and Y-markers on the second chromosome : the result shows that recombination does not occur, because moths depositting B-grey, variant and collapsing eggs segregated with 1 : 2 : 1 ratio (see Table 7). 5. Separation of the components of the collapsing and the normal eggs by centrifugation (14,500 g, 40 min.) shows no significant difference. The reason for collapsing is, therefore, attributed not to the lack or reduction of any components in the egg, btit to the structural abnormality of the egg shell. 6. Phase-contrast microscopic observations of surfaces and cross-sections of the egg shells are carried out on various genic combinations (Gr/Gr, Gr/+, Gr/Gr^col, Gr^col/Gr^col and +/+). The surfaces of abnormal eggs are common in the irregularities of the patterns which were copied when the exochorion had been secreted and further, in the cross-sections significant differences in the thickness of the shells and irregularities of the outer- and mid-layer structure are seen (Plate 22. 1-5). From these investigations as well as informations about grey eggs up to present, it is postulated as follows : I. The egg shape is determined by the pattern of the form and arrangement of follicle cells at the ovarian differentiation and the chorion substance is secreted by them. Then, it is expected that the shape of the egg as well as the physiological function of the follicle cells become abnormal as described above, if the Gr or Gr^col genes begin to act at relatively early stages of ovarian development, before the determination of the pattern of follicle cells. On the contrary, in other grey eggs with no abnormalities in shapes, the genes causing these characters are possibly not at work until the pattern of follicle cells is determined. Such a relationship between the time of genic action and the resulting characreristics is very interesting from the developmental point of view. II. In the case of Toyama's grey egg, phenotypic difference between the eggs laid by Gr homozygous and heterozygous female is explained as an example of socalled incomplete dominance of genic action for chorion formation. And this is also the cases of Kei's grey egg, Grk (Kei, 1937, 1943), and White side egg, Se (Kei, 1933, 1937, 1943). III. Although the authors could not find out the pseudoallelic relation between Gr and Gr^col genes, there remains a possibility that Gr multiple allelic series including Gr, Grk, Gr-16 and Gr^col (and possibly Grl, Gr-1, Gr-2, Gr-6) genes may constitute a complex nature of the locus. Because, it seems, from the developmental point of view of the genic action of these multiple allelic genes, that there are at least two groups : one is characterized by the abnormalities of the egg shape as well as chorion formation, and the other only by the chorion formation.
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