ISSN 1022-7954, Russian Journal of Genetics, 2014, Vol. 50, No. 2, pp. 161–167. © Pleiades Publishing, Inc., 2014. Original Russian Text © M.V. Modorov, 2014, published in Genetika, 2014, Vol. 50, No. 2, pp. 181–188. 161 INTRODUCTION In September 1957, there was a major radiation accident (total emission of radioactive waste 74 PBq) at the production association “Mayak” (Southern Urals). A territory with contamination of 90 Sr over 74 kBq/m 2 was called the East-Ural Radioactive Trace (EURT); its area was 997 km 2 with a width of 8–9 km [1]. Ecological and genetic studies of small mammals of EURT began in 1962 and still continue. A number of data points to the fact that the potency of at least two factors determining the genetic structure of animal populations has changed as a result of radioactive con- tamination of the territory: the mutation process [2– 4] and natural selection [5]. It is of interest to analyze the consequences of such changes. Perhaps they have led to a shift in the frequency of alleles and an increase in the genetic diversity parameters or were compen- sated. Previously, we analyzed the allozyme variability of the Ural field mouse that inhabits the EURT zone [6]. It was shown that the pattern and frequencies of alloz- ymes in animals caught in the impact and control areas are similar. Unsubstantiated extrapolation of this result to other rodent species, in our opinion, is unjus- tified, since there are interspecific differences in radi- osensitivity, habitat preferences, and migration activ- ity. In this paper, we analyze the allozyme variability of the northern red-backed vole Clethrionomys rutilus Pallas, 1779, which, like the Ural field mouse, is one of the most frequently used objects for studying the EURT biota [2, 5, 7, 8]. To assess the impact of the radiation factor on the rate of the mutation process, we calculated radiation doses received by rodents that live in the contaminated area. MATERIALS AND METHODS Sites and Methods of Trapping The animals were caught using live traps in snow- free periods of 2005–2011 at nine sites. The impacted areas are located on the central axis of EURT on the southern shores of the lakes Berdenish (55°46′ N, 60°52′ E) and Uruskul’ (55°49′ N, 60°55′ E). The sites “Metlino” (55°48′ N, 60°00′ E) and “Druzhnyi” (55°48′ N, 61°20′ E) lie in areas adjacent to the eastern boundary of the trace. As control samples, we used animals caught in the territory of the Urals with a background level of radioactive contamination. The sites “Serga” (56°30′ N, 59°15′ E), “River Uy” ( 54°01′ N, 60°59′ E) and “Sysert’” (56°36′ N, 61°01′ E) are at a distance of more than 90 km from the test grounds. In the Kurgan region, the animals were caught in the vicinity of the village Zverinogolovskoe (54°28′ N, 64°51′ E) and the village Uspenka (54°47′ N, 66°22′ E). Moreover, as an external control, we used bank voles (Clethrionomys glareolus Schreber, 1780) from the sites “Sysert’” and “Serga”. Radiation Dose Rates Estimation and Allozyme Variability in the Population of the Northern Red-Backed Vole (Clethrionomys rutilus) from the East-Ural Radioactive Trace M. V. Modorov Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620144 Russia e-mail: mmodorov@gmail.com Received May 20, 2013 Abstract—The paper estimates the external (due to radionuclides accumulated in the soil) and internal (due to incorporated radionuclides) exposure of rodents that live in the head of the East Urals Radioactive Trace (EURT). It is shown that in the last decades the dose rates were lower than the values that lead to a doubling the number of mutations in the allozyme loci in mammals. The variability of the eight allozyme loci in pop- ulations of northern red-backed voles from the EURT zone and their neighboring plots, as well as the terri- tories of the Urals and Trans-Urals with background levels of radioactive contamination, are analyzed. No differences in the pattern and frequency of allozymes that would distinguish the EURT samples from a num- ber of other populations of the Urals, were found. In the control sample “Sysert’,” “unique” for the Ural pop- ulations of northern red-backed voles, alleles of the loci Got and Sod were marked, conspecific to a closely related species—the bank vole. This fact can be regarded as evidence of recent cross-species hybridization. DOI: 10.1134/S1022795414020094 ANIMAL GENETICS