Arranged wizard marriages?

[jdr0918]

No: HPFGUIDX 96703

<<<In HPforGrownups at yahoogroups.com, "Jim Ferer" wrote: ...This 
brings up a problem that intermarrying groups eventually get into
... the danger of genetic diseases like haemophilia or even Tay-Sachs 
disease. ...How do the Purebloods avoid it?  Do they have magical 
help? We'll never find out, but you do wonder about it.>>>

The Sergeant Majorette says

I don't believe they *have* avoided it. Low fertility rates (the 
Weasleys being a notable exception), mental illness (tell me Sirius 
isn't bipolar, and that mother! And Bellatrix!), pallor and physical 
delicacy... As Ron points out, wizards have to mix with Muggles, or 
they'd have died out.

I wouldn't be surprised to find that the scientific ill-advisedness 
of inbreeding becomes a plot point in the last books.

--JDR