G-band homology and C-band variation in the Japanese mustelids,Mustela erminea nippon andM. sibirica itatsi

The diploid number(2n)and fundamental number (FN) were 44 and 64 inMustela erminea nippon and 38 and 64 inM. sibirica itatsi. In spite of such a marked dissimilarity in their chromosome constitution, most of the chromosomes of these two species showed high G-band homology. On the other hand, interspecific variations in the amount of C-heterochromatin were observed in several pairs of chromosomes which were regarded, based on their G-banding patterns, to have arisen from a common origin. Some of the chromosome pairs associated with the C-heterochromatin variations showed significant differences in length or arm ratio, whereas others did not. These findings strongly indicate that the G-banding patterns might have been well conserved, at least in the euchromatic regions, through the speciation process; in contrast, C-heterochromatin showed quantitative variations, some of which could be regarded to have been formed by duplication. Thus, the karyological relationships between the Japanese ermine and the Japanese weasel could be explained by Robertsonian fusion and quantitative alteration of C-heterochromatin.