Proceedings of the Japan Academy, Series B

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The karyotype and G-, C- and N-banding patterns of the Japanese water shrew, Chimarrogale platycephak platycephala, have been examined for the first time. The karyotype is characterized by a diploid number of 52 and by an FN (fundamental number) of 100. The sex chromosomes are of the XX(_??_)-XY(_??_) type usual in mammals. The pair no. 1 carries a pronounced secondary constriction on the proximal region of its short arm which functions as a nucleolus organizer, as confirmed by AgI staining. No. 1 chromosomes are also noteworthy in that their short arms distal to the secondary constriction are totally heterochromatic and these arms are significantly different in their length, regardless of the sex, constituting a heteromorphic pair.
The phyletic relation between the Japanese water shrew and the European water shrew, which are included in different subfamilies in the present taxonomic system, has been discussed on the basis of their karyological similarity.

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The distribution of the chromosome number and the karyotype in 18 spontaneous mammary tumors developed at the inguinal regions of the male soft-furred rat (Millardia meltada) are analysed. Among them 17 tumors show a modal occurrence of 50 chromosomes which are the normal chromosome number of this species. The karyotype of the tumor cells is not different from the normal somatic cells. One specimen has 51 chromosomes among which one trisomy (no. 16) is included. The normal karyotype of the tumor cells does not change during 10 passages in vitro cultivation. Based on the karyotype analysis the mammary tumor of the soft-furred rat is suggested to be a benign type depending on the male hormone. Table I. Chromosome number distribution of the 18 mammary tumors developed in the males of the soft-furred rat

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Chromosomes of a methylchoranthrene induced tumor in the soft-furred rat are analysed. The chromosome numbers are distributed widely from 40 to 150 or more. In this tumor the chromosome number variation is due to the nondisjunction and the Robertsonian fusion. The malignant tumor with the anormous chromosome alteration is in comparison with the benign mammary tumors with the normal karyotype observed in this animal.

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Lymphocytes from four normal controls and from four patients with TS are studied for SCEs and the cell cycle kinetics in the MMC-treated cultures. The results reveal that TS lymphocytes have almost the same proliferative kinetics and SCE frequencies as normal cells both in untreated cultures and when exposed to MMC.

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