Banding pattern analysis of polymorphic karyotypes in the black rat by a new differential staining technique

Polymorphic karyotypes of black rats (Rattus rattus) collected in Japan, Australia and India were analysed by a new differential staining technique by which banding patterns in the metaphase chromosomes are revealed. The technique consists in two steps: immersion of slides in a mixture of 2 x SSC and 0.1% (w/v) SDS (sodium dodecyl sulfate) for a few seconds at room temperature, and staining in Giemsa. By this treatment characteristic banding patterns were obtained in each chromosome pair. From the banding pattern analysis, subtelocentric pairs No. 1 and 9, which are polymorphic in respect to the acrocentrics and the subtelocentrics, were proven to have originated by pericentric inversion in the acrocentrics. The origin of two large metacentrics observed in Australian and Indian black rats was confirmed to have been developed by Robertsonian fusion of the acrocentrics No. 4 and 7 and No. 11 and 12 present in the Asian type black rat.Contribution No. 873 from the National Institute of Genetics, Japan. Supported by a grant-in-aid from the Ministry of Education of Japan (Nos. 92159 and 92332).