Abstract
Differences in the number of chromosomes with secondary constrictions and in the size of the C-band region on certain chromosomes have been observed among the following inbred strains of Mus musculus: C57BL/10J, C57BR/cdJ, DBA/1J, CBA/J, BALB/cJ, and AKR. These differences are useful as indicators of the location of rRNA genes and as normal chromosome markers. The size of each C-band region appears to remain constant over many generations. Only one probable change in the size of a C-band region was found.