抄録
Karyotypes and distribution of B-chromosomes in four youngs from one litter are examined. They have the same basic karyotype with 2n=38. The Robertsonian fission is not observed in these specimens. Among four specimens, two specimens, RD-8404 (_??_) and RD-8406 (_??_), have the modal number of 2 B's, but the other two, RD-8405 (_??_) and RD-8407 (_??_), show to have 3 B's. The somatic variation of the number of B's is observed in these four specimens, but is slightly different from each other. The difference of the number of B's in these specimens is suggested to be due to the random distribution of B's in meiosis of the parents.
