THE ORIGIN OF THE BROWN FROGS WITH 2N=24 CHROMOSOMES

Late replication and C-banding analyses of somatic metaphase chromosom es were attempted on three species of brown frogs with 2n = 26 chromos omes (Rana japonica, R. tsushimensis and R. temporaria), and three wit h 2n = 24 chromosomes (R. ornativentris, R. dybowskii and R. chensinen sis), which are distributed in the Palearctic region. The late replica tion banding patterns were highly conserved in these species. Four chr omosome inversions were demonstrated in R. ornativentris, two in R. dy bowskii and two in R. tsushimensis. From a detailed comparison of late replication and C-banding patterns between the 2n = 26 and the 2n = 2 4 species, it was found that an end-to-end fusion of two small chromos omes (nos 11 and 13) in an ancestral 2n = 26 species may have produced the medium-sized no. 6 chromosome of the 2n = 24 species.