Robertsonian translocation in the house mouse: a tale of chromosomal speciation

The subspecies Mus musculus domesticus has a very high chromosome number variability for the presence, in different populations, of different numbers of metacentric chromosomes. These metacentrics are derived by Robertsonian fusion, i.e. the joining of two acro/telocentrics at the centromeres. Since the discovery in 1969 by Alfred Gropp of the first chromosomal variant in an isolated mouse population of the Swiss Poschiavo Valley, more than 100 geographically distinct chromosomal races with metacentrics fixed in homozygosity have been described. The friendship and the common scientific interests among Alfred Gropp, Ernesto Capanna and Maria Gabriella Manfredi Romanini have primed a wealth of studies on the “Robertsonian phenomenon” in this species. These studies have contributed to elucidate i) the molecular bases of metacentric chromosomes formation, ii) the establishment of metacentric races and iii) the impact that chromosome heterozygosities exert on reproductive isolation and speciation.