On a spontaneous mosaicism observed in the silkworm egg

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Among the larvae of silkworm spontaneous mosaicism is not a rare occurrence and it is known to be highly accererated by some agents such as X-rays, temperature shocks, centrifuging and other extreme treatments. In the egg of this insect, however, spontaneous mosaicism has never been recorded even though several colouring genes had been known. As was previously reported, the present author has succeeded to obtain mosaic eggs by means of high temperature shock. Since then, he paid constant attention to find out mosaics in thousands of eggs, and succeeded, fortunately.From a crossing of (Be2/Be2, re/re, Z+/W_??_×be2/be2, Re/Re, Zos/Zos_??_) F2 offspring is expected in a ratio of 9 black: 4 red: 3 brown. Among these F2 eggs two mosaics were found, which is shown in Fig. 1. As is clearly seen in the figure, anterior part of the egg was covered by red serosa cells and posterior by black cells, thus belong to an antero-posterior mosaic type. One of these two eggs (ms. 1) hatched out and completed its life cycle. The resulted caterpillar from this egg was a mosaic, whose left half of the body was os-translucent, while the other part was wholly normal. Therefore, it belongs to a bilateral type. The moth was, also, bilateral mosaic having black right and red left eyes. This individual was a female but laid no eggs after mating. As the plane of bilaterality of the embryo corresponds to the plane of symmetry of the egg, the antero-posterior mosaic egg ought to give rise to the same mosaic type in the caterpillar as well as in the moth. In the present case, however, the mosaic caterpillar and moth, resulted from the mosaic egg, was bilateral mosaic. Disaccordance of mosaic planes in the egg and later life remains unexplained.
日本遺伝学会の論文

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田島彌太郎
蠶絲試驗場熊本支場

On a spontaneous mosaicism observed in the silkworm egg

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