Multiple Chromosomal Polymorphism in Birch Mice of the Subtilis Group (Rodentia, Dipodoidea, <i>Sicista</i>) from Saratov Right Bank

Abstract

Cytogenetic analysis (routine, G-, C-, AgNOR-chromosome banding) allowed to obtain new data on chromosomal polymorphism in the population (n = 13) of Sicista sp. 1, representative of the Sicista subtilis group from the Saratov Region, right bank of Volga River. It was shown that in the studied polymorphic population of a species from the northern part of the species' range (Voskresensky district of the Saratov region) the diploid number of chromosomes varies from 2n = 22 to 2n = 24, and the number of autosome arms from NFa = 39 to NFa = 44, and the sample includes the following 6 karyotype variants: with 2n = 24, NFa = 44; 2n = 24, NFa = 43; 2n = 23, NFa = 40; 2n = 23, NFa = 41; 2n = 22, NFa = 39; 2n = 22, NFa = 40. Based on G‑banding method, the determined intrapopulation chromosomal polymorphism in Sicista sp. 1 was defined by two chromosomal rearrangements: tandem translocation involving two biarmed autosomes No 4 and 10 and a pericentric inversion of pair No 6. In the studied sample (n = 13), a stable advantage of heterozygotes was revealed for both structural chromosomal mutations and the chromosomal polymorphism is characterized as balanced or heterozygous. The potential role of the identified polymorphism in chromosomal evolution and adaptive strategy of the species is discussed.