Studies on the Karyotype and Serum Transferrin in the Ceylon Black Rat, Rattus rattus, having 40 Chromosomes

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The karyotype and electrophoretic pattern of serum transferrin were examined in 18 black rats (Rattus rattus) from Kandy, Sri Lank (Ceylon). Ten rats (5_??_ and 5_??_) were karyotyped based on air drying from bone marrow cells and the consistent count of 2n=40 was obtained. The somatic complement contained one outstandingly large metacentric pair. The metacentric pair seemed to have resulted from the Robertsonian fusion of acrocentric pairs No. 11 and 12 which were present in the Asian type black rat. Four kinds of transferrin band, Tf-C₁, Tf-C, Tf-D and Tf-E were demonstrated. There was detected no Asian type transferrin (Tf-R and Tf-N) in all rats examined. Evidence presented strongly suggests that the Ceylon black rat is not originated from the hybrid between the Asian (2n=42) and Oceanian type (2n=38), but is evolutionally transient type from the Asian type to the Oceanian.