@saab,
There is absolutely no question culture influences our life much more than DNA. The child of a couple born in, say, Canada, of German immigrant parents will have a life much more like his fellow Canadian whose parents came from Italy or Korea than he will with the people of Germany. However, genetically he will still be like he was if his parents stayed in Germany.
The trick, however, in a diverse country like Canada, is to find someone of pure German descent to marry, (assuming the German Canadian child cares about such things). Since immigrants from different countries tend to "adopt" certain neighborhoods in cities when they come, that might even happen for the first generation. The German-Canadian guy marries the girl next door who is also of German descent. However, who
their kids will marry is quite possibly not to be of pure German descent. When the immigrant moves to a new country, the bloodline, so to speak, doesn't stay pure for too many generations. And even if the third generation marries someone of similar ancestry, (the immigrant is the first generation, the kids born in the new country are the second generation, their kids are the third generation, etc), the chances of the fourth generation marrying someone of pure German descent is pretty low.
DNA doesn't determine their behavior, not by a long shot. But it does determine their inherited traits.