Karyotype and Molecular Genetic Differentiation of a 24-Chromosomal Form of the Gray Hamster Nothocricetulus migratorius from the Tien Shan

— The widespread Palearctic rodent species gray hamster Nothocricetulus migratorius has a karyotype with a stable number of chromosomes 2 n = 22 throughout the entire range of its habitat. We found gray hamsters with diploid number of chromosomes 2 n = 24 locally distributed in the Qurama Ridge of the Tian Shan. A new karyotype and analysis of G- and NORs-bands of differentially stained chromosome sets were described for the first time. The described karyotype differs from the 22-chromosomal karyotype of gray hamsters by the Y-chromosome morphology and the presence of an additional pair of heteromorphic small chromosomes. Molecular genetic analysis revealed genetic divergence of 24- and 22-chromosomal forms of N. migratorius , and the differences between them in mitochondrial markers are comparable and in terms of nuclear markers exceed the differences between C. barabensis (2 n = 20) and C. psevdogriseus (2 n = 24). The data obtained give grounds to discuss the taxonomic status of the 24-chromosomal form of gray hamsters from the Qurama Ridge and consider the differentiation of N. migratorius karyomorphs as a stage of chromosomal speciation.