Dynamic of the B Chromosome System in the Population of the Korean Field Mouse Apodemus peninsulae (Mammalia, Rodentia) in the Northern Region of the Pritelets Taiga of the Altai Mountains over a 36-Year Period.

The process of changes in the number and morphology of B chromosomes in the populations of mice (Apodemus peninsulae) in the northern region of the Pritelets taiga of the Altai Mountains over a 36-year period (1978‒2014) was traced. Three time phases were distinguished. From 1978 to 2002 (24 years)—a phase of steady growth of the number of B chromosomes, with a relatively uniform average increase of 1.4 chromosomes per decade (from 3.17 ± 0.2 to 6.5 ± 0.54); the phase of stabilization of the indicator when it consistently ranged between 6.3 and 6.9 (2002–2012), although the indicator was at least doubled compared to early 1980s (differences are significant); and the third period (2012‒2014) of the emerging trend of decrease in the number of supplementary chromosomes (differences are also significant). The change in the conditional mass index of B chromosomes (mB) also had similar dynamics, and it was at its maximum for the species during the period of stabilization. The dynamics of different morphotypes of B chromosomes showed an unequal contribution to the overall dynamics. The main contribution was made by large, medium-sized, and small metacentric B chromosomes. Micro-B chromosomes and acrocentrics were absent in the growth phase and appeared in the stabilization phase at the maximum of other indicators. [ABSTRACT FROM AUTHOR]