The Robertsonian phenomenon in the house mouse: mutation, meiosis and speciation.

Many different chromosomal races with reduced
chromosome number due to the presence of Robertsonian
fusion metacentrics have been described in western Europe
and northern Africa, within the distribution area of the western
house mouse Mus musculus domesticus. This subspecies of
house mouse has become the ideal model for studies to
elucidate the processes of chromosome mutation and fixation
that lead to the formation of chromosomal races and for
studies on the impact of chromosome heterozygosities on
reproductive isolation and speciation. In this review,
we briefly describe the history of the discovery of the
first and subsequent metacentric races in house mice;
then, we focus on the molecular composition of the
centromeric regions involved in chromosome fusion to
examine the molecular characteristics that may explain
the great variability of the karyotype that house mice show. The influence that metacentrics exert on the nuclear
architecture of the male meiocytes and the consequences on
meiotic progression are described to illustrate the impact
that chromosomal heterozygosities exert on fertility of
house mice—of relevance to reproductive isolation and speciation.
The evolutionary significance of the Robertsonian
phenomenon in the house mouse is discussed in the final
section of this review.