Pure Blood Parentage

[Emily Rose]

No: HPFGUIDX 75758

> Message: 19
>  Date: Wed, 06 Aug 2003 15:52:33 -0000
>  From: "clarinut76" <clarinut76 at yahoo.com>
> Subject: Pure Blood Parentage
> 
> 
> How long are you a half-blood?  I mean, if James was born from two
> wizards, he'd be a pure blood (we've never heard mention anything
> different) and Lilly seems to come from a muggle family (lots of
> debate on this, I'm sure...).  Harry is considered a half-blood for
> this reason, but since he's born of a wizard and a witch, couldn't he
> be thought of as a pure blood?  Is the muggle blood thing always
> there?


Interesting question.

I always thought of it like royalty.  Royal blood lines intermarried each
other so that royalty could always marry royalty.  However, when Prince
Charles married Diana, she was the daughter of an Earl.  Therefore she was a
peer, but not a royal.  Once married she became "Princess Diana" and her two
sons, the offspring of a royal and a peer with a royal title, are Princes.
Anyone who marries Prince William, will gain the title of Princess because
he is of royal blood.  However, when Diana divorced Charles, she kept her
princess title, but any other children she bears will be peers, not royals.

Sirius's family tree reminds me of a royal family tree though magical vs.
muggle born seems more complicated since it is based on certain abilities
rather than titles.

It's even weirder if you think about it from a genetics point of view.
Let's say there is a gene for magical ability.  Genes come in pairs because
you get one half from your mother and the other half from your father.  It's
going to get ugly.  Ready?  Here we go...

If the gene for magic is recessive then the gene for non-magic is dominant.
Therefore, if pure blood families are "true breeding" (offspring always have
magical ability) it means that all the dominant non-magic genes have been
bred out so all there are only recessive magical genes - pure bloods can
only have more magical offspring.  This means that it would be impossible
for a squib to be born to a witch and a wizard because neither would carry
any dominant non-magical genes.  A Squib could only be born if a witch or
wizard married a muggle with at least one dominant non-magic gene  (Remember
you need 2 recessive magical genes for magical ability to be present).  A
squib would carry a recessive magical gene and a dominant non-magic gene
making it possible for the squib to give birth to magical offspring if they
coupled with a witch or wizard.

In Hermione's case, she is a magical child born of muggles meaning that both
her parents are "carriers" of a recessive magical gene; in other words they
have a 1 in 4 chance of having magical offspring.  A muggle carrier would
have the same two genes as a squib by the way:  one recessive magical and
one dominant non-magical.  In the case of Harry's parents, both of them
carry only recessive magical genes meaning there was a 100% chance that
Harry would have magical ability - just like in a pure blood family.  It
also means that like Hermione's parents, Petunia's parents were both
carriers of magical genes meaning that Petunia could be a carrier too.  If
that is the case, there is a 50% chance that so is Dudley.  So depending on
the type of person who would marry and have children with Dudley, there is a
possibility that the Dursley's could have a grandchild at Hogwarts someday.

This doesn't work the other way around because if magical ability was the
dominant gene, then there would be hardly any muggles and "pure blood"
families wouldn't breed true.

Personally, I think it's best not to think about any of this when reading
the books.  :-)

-e