Mapping of rRNA gene loci in the mice, Mus musculus molossinus (Japan) and Mus musculus musculus (Russia) by double color FISH.

Ribosomal RNA gene (rDNA) loci of Russian Mus musculus musculus and of Japanese Mus musuculus molossinus were mapped by double color FISH. The total number of rDNA loci was varied from 5 to 12, although the loci on chromosomes 12, 15, 16, 18, and 19 were common to all mice examined. Instead, polymorphisms of the rDNA loci were found on chromosomes 1, 5, 8, 9, 10, 11, 13 and 17. The novel rDNA loci of M. m. musculus were found in Nov/TUA strain on chromosomes 8 and 17. These observations, together with those of previous reports, suggest that the rDNA loci of Mus musculus species are in the evolutionary process of further translocation to other chromosomes.