The Japanese Journal of Genetics

Inheritance of the“Additional Crescent” Mutation in the Silkworm

Kan-ichiro SUZUKI, Shin-ichiro OHTA

1930 Volume 6 Issue 1 Pages 1-13
Published: 1930
Released on J-STAGE: November 30, 2007

DOIhttps://doi.org/10.1266/jjg.6.1

JOURNAL FREE ACCESS

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The normal silkworm larva is furnished with a pair of large“crescent” marking (“lunules”) on the second abdominal segment, and a pair of small“star”marking on the fifth segment.
A single“additional crescent”larva appeared as a mutation in the F₁ generation from the cross Japanese race No. 109 _??_×Chinese race No. 102 _??_ reared in 1926. This individual had two pairs of large “crescent”marking, one on the second abdominal segment, as usual, and another pair on the third segment, while the“star”marking was entirely absent from the fifth segment.
The new type has been preserved and propagated by crossing the mutant to the normal strain, but the characteristic has never bred true, segregating the normal type in a number of about one third of the total offspring. This fact can be explained as due to the lethal function of the “additional crescent”gene, which may be represented by the symbol Ca. About one fourth of the embryos produced by mating of“additional crescent”males and females are killed just before the hatching. The killed embryos were undoubtedly homozygous with respect to the Ca gene. This is why the“additional crescent”does not breed true. The same result is obtained in absence of P gene (normal gene allelomorphic to the“plain”) and presence of Ca, where is no“additional crescent” marking visible.
In short, Ca is a dominant mutation which is lethal when homozygous, regardless of that the“additional crescent”character is externally visible or not.

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Über Parthengenesis bei Houttuynia cordata

S. OKABE

1930 Volume 6 Issue 1 Pages 14-19
Published: 1930
Released on J-STAGE: November 30, 2007

DOIhttps://doi.org/10.1266/jjg.6.14

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1. Die somatische Chromosomenzahl von Houttuynia cordata beträgt 94-98.
2. Bei der Kernteilung der Pollenmutterzellen treten einige Univalenten und viele Gemini auf und die Reduktion der Chromosomenzahl wird unregelmässig ausgeführt.
3. Es gibt zwei Typen der ersten Kernteilung in der Embryosackmutterzelle. Bei einem Typus treten einige Univalenten und viele Gemini auf wie bei den Pollenmutterzellen, und bei dem anderen kommen alle Chromosomen als Univalenten vor, und keine Reduktion der Chromosomenzahl wird ausgeführt.
4. Die Eizelle des diploiden Embryosackes entwickelt sich ohne Befruchtung, also ganz parthenogenetisch zum Embryo.

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Karyological observations in different interspecific hybrids of Brassica

Tsunetaro SASAOKA

1930 Volume 6 Issue 1 Pages 21-32
Published: 1930
Released on J-STAGE: November 30, 2007

DOIhttps://doi.org/10.1266/jjg.6.21

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1. The karyological study in the hybrids of the following combinations were carried out.
Group 1. B. Napus, L. var. Napobassica, REICHB. n=19_??_×B. pekinensis, RUPR. n=10 _??_ B. Napus, L. var. Napobrassica, REICHB. _??_×B. nipposinica, BAILEY, n=10 _??_ B. Napus, L. var. oleifera, DC. n=19 _??_×B. rapa, L. n=10 _??_ B. pekinensis, RUPR. n=10 _??_×B. Napus, L. var. oleifera DC. n=19 _??_
Group 2. B. Napus, L. var. oleifera DC. n=19 _??_×B. Napus, L. var. oleifera DC. n=19 _??_ B. Napus, L. var. Napobrassica, REICHB. n=19 _??_×B. Napus, L. var. oleifera, DC. n=19 _??_
Group 3. B. Napus, L. var. Napobrassica, REICHB. n=19 _??_×B. juncea, COSS. n=18 _??_ B. juncea, Coss. n=18 _??_×B. Napus, L. var. Napobrassica, REICHB. E=19 _??_
2. The meiosis of the pollen mother cells are very similar in every hybrid of group 1. 10 bivalents and 9 univalents appearing in the heterotype division. After the bivalents were separated and passed to the pole normally, the univalents distributed irregularly with the splitting of a few chromosomes. Homotype division was carried on normally, though in a few cases the lagging chromosomes and the splitting of the univalents were observed. Restitution nucleus was found sometimes.
3. With the hybrids of the combination in group 2, no abnormality in the meiosis of the pollen mother cells was observed. 19 bivalents appeared in the heterotype division and the chromosomes were distributed normally in the heterotype and homotype divisions.
4. 10 bivalents and 17 univalents appeared in the heterotype division of the pollen mother cells of the hybrid group 3. After the former passed to both poles normally, the latter were distributed irregularly with the splitting of some chromosomes. In the homotype division, the general feature was normal though some lagging chromosomes and splitting of halves of chromosomes were to be seen. The occurrence of large nuclei and dyads, however, were also observed in a few cases.
5. Abnormal meiosis as in the F₁ progenies of group 1 and 3 was also observed in the F₂ hybrids of B. Napus, var. oleifera×B. pekinensis and B. juncea×B. Napus, var. Napobrassica. The number of the bivalents was the same or more and the univalents less than in the F₁ progenies. In the heterotype division of B. juncea×B. Napus, var. Napobrassica the chromosomes were sometimes supernumerous. The polyads, from dyads to hexads, were also formed in F₂ hybrids. Univalents often occurred in a ring in F₂ progenies of B. juncea×B. Napus, var. Napobrassica. The number of univalents in a ring was less than those of F₁ progenies. Some univalents of F₂ progenies of B. Napus, var. oleifera×B. pekinensis were also arranged in a ring though the arrangement was rather irregular.

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