Harry Potter 7(Don't click if you are planning on reading the book - SPOILERS)

[Stargate525]

[spoiler= On a related note...]
Did anybody else notice how all the families seemed to be related somehow?
[spoiler=To note]
* Gaunts and Potters both come from a Perevell line
* Arthur Weasley's mother's maiden name was Black
* Gaunts were descended from Slytherin[/spoiler]

Also, looking at the Black family tree on wikipedia, I found the following [spoiler=names]
* Sirius Black (of course)
* Bellatrix Black (married to a LeStrange)
* Andromeda Black (married to Ted Tonks)
* Narcissa Black (married to Lucius Malfoy)
* Septimus Weasley (married to Cedrella Black, son named Arthur)

And references to the names Potter, Crabbe, Longbottom, Yaxley, Macmillan, and others.[/spoiler]

In other words, whether through blood or marriage, there's relatively few characters that aren't somehow related to a bunch of other characters.[/spoiler]

Well its the factor of the blood being so limited. It's akin to the royal lines of Europe in the 15-18th centuries.

[Wensleydale]

[spoiler]Yes, the Potters appear to stem from both Blacks and Peverells.

Which might explain why any hexes to prevent one not of the black family line possessing the house didn't fire off on Harry.[/spoiler]