> Humans can and do carry certain "bad" genes that could potentially cause serious defects in their offspring.

Quite right, I should have mentioned that, thanks.

> Unfortunately, I don't know of any examples off the top of my head of exactly what kinds of defects tend to happen in those cases. Anyone else have some?

I know Sickle Cell Anemia requires paired genes like that. And the British Royal Family has several hereditary problems associated with inbreeding, but a quick google didn't find anything.

Edit: The British line does suffer from Heamophilia, a genetic disorder, but it is not triggered by two recessive genes (called autosomal recessive inheritance) so has little bearing on this little side tangent. But Albinoism and Cystic fibrosis are two other genetic trait that requires two recessive genes to manifast though: http://www.bidmc.harvard.edu/obgyn/genetics_carriers.asp

You know, I love the web. How the hell would I have found this information without it? Anything I want to know about, it's a mouse click away. That is so awesome, it makes me all teary-eyed.