On an interesting side note, it says on the german wikipedia site (and this is something that is also mentioned on a couple of books) that the two male grandsons of Goethe, both of them brothers, were homosexual. What are the odds of that? Needless to say they didn't leave any issue, and their only sibling, a girl, died at a very young age.
A peculiar case, which at the same time gives one piece of evidence for a little theory that I have: that, while talent is undoubtedly hereditary, genius is not, and after concentrating itself on a single individual, the rest of his lineage tends to annihilate itself afterwards.