Evolution of the chromosomal races of Mus musculus domesticus in the Rhaetian Alps: the roles of whole-arm reciprocal translocation and zonal raciation

The evolution of ten Robertsonian (Rb) races of the house mouse (Mus musculus domesticus) in the Rhaetian Alps of northern Italy and southern Switzerland is reconsidered. The mechanisms of centric fusion, zonal raciation and, for the first time, whole-arm reciprocal translocation (WART), are used in this non-mathematical approach to produce a phylogenetic tree (using chromosome fusions as characters) with the smallest number of steps. The shortest tree that we found (16 steps) is at least two to nine mutations shorter than previously published models. Three other trees (17 or 18 steps) are also considered, since they are geographically more sensible. In general, these four scenarios correspond more closely to the present distributions of the ten Rb races than previous trees. Our results suggest that zonal raciation and WARTs play an important role in the evolution of Rb races of the house mouse.