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The present study of green frog hybrid populations of Ukraine, including analysis of allozyme variability and planimetric analysis oferythrocytes size has confirmed that the unique region in this area is the Severski Donets basin The allopolyploid individuals there are met very frequently (5.7% of all investigated frogs). In other areas of Ukraine only two polyploid hybrids have been recorded. Beside that, one frog was defined as triploid Rana ridibundus. According to our investigations, all triploid hybrids from the Severski Donets basin are identified as P. esculentu (=lessonae)--2 ridibundus males.

Research of the alleles of the species-specific genes in the gametal cells of Rana kl. esculenta hybrids proved the existence of three local populations within the territory of Ukraine. Their hybrids reject either the genome of lake frog (Danube lowland), either the previous one or another one genome (basin of Severskiy Donets river), either the genome of pond frog (the residuary territory of the areal). The research of skin transplants rejection of hybrids' parental species has shown that despite the orientation of genome elimination of this population the graft of lake frog always starts identifying and rejecting earlier. That is why the genetic skewness of hybrids becomes apparent at the skin level and corresponds to its manifestations at the organism level.

The biochemical genetic marking and analysis of the ploidy and sexual structure of the green frog populations from the Transcarpathian lowlands have demonstrated that this region is inhabited by the unisexual populations composed of the allodiploid females only. Their genome includes a small portion of the marsh frog genic diversity. This phenomenon is discussed in relation to the unisexual population reproduction problem. The assumption is proposed that in the Transcarpathian hybrid populations the hybrids are spawned by the parthenogenesis.

The comparative analysis of hybrid populations of toads Bombina bombina and B. variegata from Ukraine and Croatia revealed the essential differences in their genetic structure. The population composition and the direction of genetic introgression are determined initially by the ecological factors (the locality type, the country relief). The clear predominance of the red-bellied toad Bombina bombina was found in two cases: in the lowland populations and in the big samples. The second parental species, B. variegata, predominates in the highlands and in the small samples, respectively.

Population-genetic analysis of hybrid populations of green frogs from the Dnepr basin demonstrated limited gene introgression in diploid hybrids in addition to semiclonal reproduction, which is typical for Rana esculenta hybrids. Introgression is largely confined to the Ldh-B locus: the gene of R. lessonae is introduced into the R. ridibunda genome. This phenomenon is unstable as it is geographically restricted and absent in populations of the E-L type.