[High-resolution GTG-banding and nucleolar organizer regions of chromosomes of two vole species: Microtus rossiaemeridonionalis and M. transcaspicus (Rodentia, Arvicolidae)]. / GTG-okraska vysokogo razresheniia i iadryshkoobrazuiushchie raiony khromosom dvukh vidov obyknovennykh polevok: Microtus rossiaemeridionalis i M. transcaspicus (Rodentia, Arvicolidae).

With the use of the GTG-banding of prometaphase chromosomes, 503 and 402 segments were revealed in haploid chromosome sets of voles Microtus rossiaemeridionalis and M. transcaspicus, respectively. Based on a detailed study of chromosomes at different condensation levels, idiograms of M. rossiaemeridionalis and M. transcaspicus chromosomes were constructed. Sequential Ag-staining and GTG-banding allowed nucleolar organizer regions (NORs) to be localized in 16 and 11 chromosome pairs of M. rossiaemeridionalis and M. transcaspicus, respectively.

[The polyploidization characteristics of the hepatocytes of the mouse-like hamster Calomyscus mystax]. / Osobennosti poliploidizatsii gepatotsitov myshevidnogo khomiachka Calomyscus mystax.

A cytophotometric measurement of DNA content in hepatocytes of maturing mouse-like hamsters was made. Cells belonging to ordinary mammalian ploidy classes 2c, 2c x 2, 4c, and 4c x 2 made about 90% of the hepatocyte population. The share of binucleated cells wa high (about 80%), the majority of these cells being 2c X 2 hepatocytes. Binucleated cells with tetraploid and diploid nuclei occur in almost every animal. An average hepatocyte ploidy level in mouse-like hamster is 4.6c. The main peculiarity of parenchymal liver cell populations is that up 5% of hepatocytes contain 3--11 nuclei of different ploidy classes. Multinucleated cells increase in number from 1.5% to 4% within the period from one year (the age of maturation) to two years. Later on their percentage does not change. It is found that in binucleated and multinucleated hepatocytes DNA synthesis can proceed asynchronously. Asynchrony in DNA synthesis elevates as the number of nuclei increases. Among the 2c x 2 and 2c x 3 cells an uneven distribution of 3H-thymidine label can occur, respectively, in 5 and in 50% cases, whereas all the cells with more than 3 nuclei display an uneven an uneven 3H-thymidin label distribution. The formation of multinucleated cells is supposed to be associated with asynchrony in DNA-synthesis in binucleated cells and with the restitution of mitosis.

[Morphology and behavior of the sex chromosomes in meiosis in four vole species of the genus Microtus]. / Morfologiia i povedenie v meioze polovykh khromosom u chetyrekh vidov polevok roda Microtus.

Morphology and behaviour of the X and Y chromosomes of four species of genus Microtus were studied at pachytene, metaphase I and meiotic metaphase. The X chromosomes of the species varied with respect to their size and location of heterochromatic blocks. The axes of X and Y chromosomes of these species as well as Microtus agrestis never formed true synaptonemal complexes at any sub-stage of the pachytene. They approached each other at the start of the pachytene throughout to metaphase I, getting situated closely. At the end of the pachytene, they formed sex vesicle. The X and Y chromosomes kept their proximity during metaphase I, but never formed true bivalents. It is suggested that lack of synapsis of the X and Y chromosomes in the genus Microtus is the final step of evolutionary trend to reduction of the size of the pseudo-autosomal region. The abolition of restrictions on homology between the X and Y chromosomes is supposed to be a cause for the fast divergence in morphology of sex chromosomes in the genus.

[Evaluation of the degree of genetic divergence in the twin species of the common vole Microtus arvalis and Microtus subarvalis (Rodentia)]. / Otsenka stepeni geneticheskoi divergentsii vidov-dvoinikov obyknovennoi polevki Microtus arvalis, Microtus subarvalis (Rodentia).

By means of starch electrophoresis, 52 proteins and enzymes of Microtus arvalis and M. subarvalis were studied to establish the extent of their similarity. Out of 52 markers studied, 7 proteins and enzymes had different electrophoretic mobility: glucose-6-phosphate dehydrogenase (G6PD), phosphogluconate dehydrogenase (PGD), diaphorase (DP), adenylate kinase (AK), lactate dehydrogenase B (LDHB), alpha-galactosidase (GAL) and hemoglobin (Hb), which make up to 13% of all the enzymes and proteins studied. The differences found between the two species studied by electrophoretic mobility of G6PD, AK, GAL and Hb, as well as the absence of intraspecific polymorphism for the above proteins permit to consider these proteins as species-specific markers, with the help of which M. arvalis and M. subarvalis can be distinguished. It should be emphasized that intraspecific polymorphism was found for PGD, LDHB and DP in M. arvalis, while in M. subarvalis these proteins were monomorphic and identical, in their electrophoretic mobility, to one of electrophoretic variants of M. arvalis. Therefore, only one of allelic variants of PGD, LDHB and DP is species-specific. Estimation of the extent of genetic similarity based on analysis of distribution of gene frequencies for polymorphic loci of M. arvalis and M. subarvalis by means of Nei's method gave the value of 0.312, the genetic distance being 1.164. The data obtained, together with the known cytogenetic data, point to a species rank of the species studied. Moreover, in spite of the morphological similarity between M. arvalis and M. subarvalis, the estimation of genetic similarity proved to be close to that for morphologically contrasting species.