Incidence of double-band HSRs in chromosome 1 of the house mouse, Mus musculus musculus, from Oland (Sweden): a population study.

The incidence of homogeneously staining regions (HSRs) in chromosome no. 1 of Mus musculus musculus was ascertained by C-band staining on chromosomes of mice collected on the island of Oland (Sweden). A total of 157 specimens from eight localities representing three regions were analysed. Mice with enlarged chromosome no. 1, due to double-band HSRs, were found in all three regions. The overall incidence of HSR-bearing chromosomes was 6.7% in mice collected on Oland in 1988. In the two largest samples, the incidences were 14.5% (n = 31) and 3.9% (n = 76). With regard to HSR size, several different variants were present. Size differences were found for the proximal as well as for the distal HSR band. Different mutant forms were found even within one population (a single farm). The implications of these findings are discussed.