[B chromosome number polymorphism and mosaicism of the Korean field mouse Apodemus peninsulae (rodentia) in the Russian Far East].

Karyotype analysis of the Apodemus peninsulae (n = 355) from 41 trapping points from the Russian Far East made it possible to reveal B chromosomes in 87.9 % animals, where 61.7% among them were mosaics. Different levels of B chromosome numbers variability such as inter- and intrapopulational, and intraindividual (mosaicism) as well have been studied. It has been revealed that frequencies of occurrence of individuals with B chromosomes and mosaicism were not constant between different population's samples. The range of the modal B chromosome number variations and the xB index variability (from 0 to 4, xB averaged 1.67) both have been fist investigated in different samples and populations of this species. Individuals with the predominant B chromosome numbers (as a rule, 0-2) have been revealed in both groups of animals (with stable and mosaic karyotypes) but the frequency was different in the geographical regions. The spectra of B chromosome variability were wider in mosaics (0-7) in comparison with animals with stable karyotypes (0-4). High frequency of individuals with B chromosomes and with mosaicism, and their significance for the species is discussed. The adaptive role of the low number of B chromosomes (1-2) is assumed and the B chromosome system seems not to be balanced in the species in whole.