Constitutive Heterochromatin and Evolutionary Divergence of Mus dunni, M. booduga and M. musculus

Abstract

The Indian pygmy field mice are one of the most interesting groups of animals from evolutionary point of view and include two morphologically extremely similar species Mus dunni and Mus booduga which share widely common natural habitats and until recently were considered conspecific. They are closely allied to the aboriginal mice Mus musculus and are distinguished from each other only on the basis of average characters (Ellerman 1961). The predominant diploid chromosome number in all the three species is 40 but while the karyotypes of M. musculus and M. booduga with all acrocentric chromosomes are identical, that of M. dunni is distinct due to invariable presence of large submetacentric X and acrocentric Y sex chromosomes. M. dunni populations from different localities also exhibit polymorphism in the number of biarmed autosomes (Matthey and Petter 1968; Sharma and Garg 1975; Markvong et al. 1975; Manjunatha and Aswathanarayana 1979; Sen and Sharma 1980/ 1983). The close morphometric and cytogenetic alliance of pygmy mice with a species like M. musculus that has been extensively utilized in molecular genetic and immunological investigations make these an attractive choice for detailed phylogenetic considerations.