The results of the study of Y-chromosomal polymorphisms of Russian and Ukrainian population are presented for Slobozhanshina--contemporary border region, former "Wild Field" boundary, which was inhabited in XVII-XVIII centuries by both the Russians from the north and Ukrainians from the west. In general, Ukrainian and Russian populations of Slobozhanshchina genetically are very close, their set and frequency range of Y-chromosome haplogroups are typical for the Eastern Europe. But a detailed analysis of highly informative Y-chromosome markers showed that after 3,5 centuries of coexistence on the same historical territory, the both nations retain the ethnic specificity of their gene pools: Ukrainian populations are similar to the rest of Ukraine, and Russian populations are similar to the south of the European part of Russia. The genetic differences may be due to the spatial characteristics of marriage migration and the predominant ethnic environment.