Complex evolution of sex chromosomes in Gerbillidae (Rodentia).

The sex chromosomes of 11 species of Gerbillidae (Meriones tristrami, M. crassus, M. libycus, M. persicus, M. unguiculatus, Gerbillus hesperinus, G. nigeriae, G. gerbillus, G. campestris, Gerbillurus tytonis, and Taterillus gracilis) are reported. A very complex evolution of the X chromosome and, to a lesser degree, of the Y chromosome was observed, including several inversions, translocations with autosomes, and an increase in heterochromatin. The role of constitutive heterochromatin, isolating autosome and gonosome segments in translocations (thus preventing any position effect), is discussed. The sequence of rearrangements affecting the sex chromosomes is considered with a view toward establishing the phylogenetic relationship of the species studied. The tendency to accumulate the same rate type of rearrangement, namely, gonosome-autosome translocations, is another demonstration that chromosomal evolution is not random in a given group of species.