Loss of telomeric sites in the chromosomes ofMus musculus domesticus (Rodentia: Muridae) during Robertsonian rearrangements

Mouse chromosomes possessing multiple Robertsonian rearrangements (Rb chromosomes) have been examined using fluorescencein situ hybridization with the telomeric consensus sequence (TTAGGG)_n. No hybridization signals were detected at the primary constriction of Rb chromosomes. This observation leads us to conclude that the formation of Rb chromosomes in the mouse is invariably associated with the loss of telomeric regions. More significantly, a further alteration in regions flanking the primary constrictions was observed after hybridizing with a minor satellite DNA probe to Rb chromosomes. It seems likely that the breakpoints required for a Robertsonian process do not include telomeric sites exclusively but extend to the adjacent pericentromeric regions of the original acrocentric chromosomes. In contrast to previous reports, these observations demonstrate the elimination of substantial amounts of chromosomal DNA during the formation of mouse Rb chromosomes.