Ah-ha! (Pardon the Scandinavian pun )

So in Swedish, there are different words for "whose" and the genitive of "who", much like in Russian. So why exactly is it that the word(s) in German, a closely related language, are the same? Do those words in Swedish sound similar to each other? I am beginning to think that it is indeed a form that is spelled exactly the same but with no etymological relation. Of course, it could just be a special rule in German, or something.