David B posts about genetic improbabilities in movies. I had recently posted such a genetic improbability in the Dodona forum, from the first season of 24.
Another good one is from House of Sand and Fog where Ben Kingsley (Indian-British-Russian-Jewish ?) and Shohreh Aghdashloo (Iranian) have Navi Rawat (Indian-German) as a daughter.
And, what can one say about this real family from the satirical March of the Giants? Recombination in action... [or not; as David B. posts in the comments, the Judd sisters have different fathers]