In situ analysis of centromeric satellite DNA segregating inMus species crosses

In situ hybridization of biotin-labeled mouse major satellite DNA clone pMR196 was applied toMus domesticus andMus spretus chromosomes (Chr). The same karyotypes were counterstained with distamycin A-DAPI to identify AT-rich heterochromatin. Chromosomes from the laboratory mouse, C57BL/6Ros (BL/6;M. domesticus) were uniformly labeled at the centromere except for the Y, while chromosomes from the divergentMus speciesM. spretus showed little or no hybridization. Differences betweenMus species in copy number of the major satellite DNA sequence were used to identify chromosomes ofM. domesticus andM. spretus in their F₁ hybrids and to discriminatedomesticus andspretus centromeres in backross progeny. The distribution pattern of heterochromatic regions demonstrated by distamycin A-DAPI counterstaining was comparable with that of in situ hybridization with pMR196, suggesting that A-T rich heterochromatin inM. domesticus is mainly constructed by the pMR196-related sequence. The in situ technique was used to examine segregation ofdomesticus centromeres in backcross progeny obtained by mating F₁ hybrid females withM. domesticus orM. spretus males. The segregation of centromeres did not deviate from the expected among the backcross progeny from C57BL/6Ros males, whereas chromosomes withM. domesticus centromeres were prone to appear in the progeny from backcross matings byM. spretus males.