This study confirms that, showing that Northern Russians (but not Southern Russians) significantly intermarried with Finno-Ugric peoples, while Southern Russians (but not Northern Russians) intermarried with Germanic peoples. Russians were also found to be genetically tied to other Slavs and to Baltic peoples and to a lesser degree to Iranian and Turkic peoples.
Lots of Finnish contribution in the genes of Northern Russians.
Russian ethnic history inferred from mitochondrial DNA diversity - Morozova - 2011 - American Journal of Physical Anthropology - Wiley Online Library