Sex!

[Steve Bates]

No: HPFGUIDX 437

Well, sorry to disappoint, but the topic is not sex per se, but two 
things related to sex: genetics and contraception among wizards.
My theory at the moment on the "magic gene" idea is that there are 
two genes that control magic; which means there are nine possible 
genotypes: 1) MMNN, 2) MMNn, 3) MMnn, 4)MmNN 5) MmNn, 6) Mmnn, 7) 
mmNN, 8) mmNn, and 9) mmnn.  (Note: those genotypes are definitely 
not evenly distributed among the population).  For both 
genes, "magic" is dominant over "muggle", but *both* genes need to be 
magic for the person to have magical quailities.  So for a person to 
be a wizard, he or she would have to have genotype 1, 2, 4, or 5.  If 
two muggles, one with genotype 3 or 6, and one with 7 or 8, were to 
have kids, there is at least the possibility that one or more of them 
will be a wizard.  On the other hand, wizard couples with the 
following genotype combinations would be able to give birth to a 
squib: 2 and 2, 2 and 5, 4 and 4, 4 and 5, 5 and 5.  The relative 
frequency that each of these nine genotypes appear in the population 
could be anywhere in a wide range, but if one or both of the 
domninant genes (M or N) were rare enough in the population as a 
whole, people with genotypes 1, 2, 4, or 5 (i. e. wizards) would be 
as rare as the books imply.  Sorry if this is really involved; this 
is only one theory; my point is to show that it is at least 
*possible* to explain through genetics what we've seen about patterns 
of magical inheritance.  One last thing, though: if my theory here is 
true, it is obviously possible for mixed marriages to produce 
muggles; I do think that that has to be possible, if squibs from 
pureblood marriages are possible.  One reason we haven't yet heard of 
this happening might be the relative rarity of mixed marriages in the 
first place.
Just a little note about contraception among wizards, and, if it 
exists, the reason why there are so many little Weasleys: being 
raised Catholic, I can see immediately that, even in the wizard 
world, there might be people who have personal or moral reasons for 
not using contraception.  Perhaps the Weasleys feel this way.  It 
might then seem odd that they continued to refuse to use 
contraception during the Voldermort years, but if GoF is any 
indication, Arthur (and I would assume the same is true of Molly) is 
not the kind of person to back down from his principles.