Features of interpopulation variability of chromosome instability in Rana (pelophylax) ridibunda from northern Lower-Volga region

The chromosome sets of several populations of Rana (Pelophylax) ridibunda from various districts of the Saratov region with different levels of anthropogenic load were studied. The karyotype of the frogs under study has been found to be identical with that of other parts of the habitat by basic cytogenetic parameters (2n=26, NF=52). The regional features of the karyotype consist in morphometrical characteristics of sepa-rate chromosomes, in particular, the polymorphism of the 7th chromosome pair has been revealed. A de-pendence of the abnormal karyotype frequency on the reservoir pollution level has been established. E.g. the minimum number of individuals with a disturbed karyotype was observed in the reservoirs of the Na-tional Park "Khvalynsky" while the maximum one was in those of the highly urbanized territories of Sara-tov and Engels Cities.