This post quoted a webchat with JKR:

How can two Muggles have a kid with magical powers? [...]

A. It's the same as two black-haired people producing a redheaded child. Sometimes these things just happen, and no one really knows why! [...]

to which I commented

Even a brief glance at Wikipedia already explains that Red hair is a recessive trait, i.e. a single ginger somewhere far up in each parent's ancestry is enough to chance this. Is JKR seriously not aware of genetics? Now that she compares it, magical abilities might as well be a genetic trait, albeit more complicated what with Squibs...

to which xDaizu amended:

...not necessarily more complicated than redheadedness. I mean, just like blood type, it could be a single gene deciding if they produce magic midiclorians or not :)

So, what is the proper analogy to the AB0 blood type system to explain Wizards/Witches, Squibs and Muggles?

One problem I'm having in coming up with an explanation is the discrepancy between JKR's statement

"Muggle-borns will have a witch or wizard somewhere on their family tree, in some cases many, many generations back. The gene resurfaces in some unexpected places."

which suggests wizardry is simply a recessive trait, versus the statement

A Squib is a non-magical person born to at least one magical parent.

which suggests said Muggle-parents of wizards/witches are actually Squib(-descendant)s.

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    +1, but careful: "Your world-builders were so preoccupied with whether or not they could (explain it), they didn't stop to think if they should." – xDaizu Apr 20 '17 at 12:24
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    Hmm. I was going to say that the difference between squib and muggle seems largely cultural, but there does seem to be some actual distinction; you may need to resign yourself to the fact that there is no consistent explanation. Alternately, you may find the fanon I discuss over here interesting – Jason Baker Apr 20 '17 at 13:42
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    I think we're ignoring the canonical Wizards originate from Mars; Muggles from mushrooms. – ibid Apr 20 '17 at 14:16
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    @ibid - That's a book written (in-universe) by a pureblood supremacist quack. It's about as relevant to actual magical inheritance as Time Cube is to real physics. – Adamant Apr 20 '17 at 15:54
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    "Is JKR seriously not aware of genetics?". Why do you find this hard to believe? – DJClayworth Apr 20 '17 at 16:32

Muggleborns have a distant magical relative, usually a squib who married a muggle. This is a quote from Harry Potter wiki:

Muggle-borns inherit magic from a distant ancestor; they are descended from Squibs who have married Muggles and whose families had lost the knowledge of their wizarding legacy. The magic resurfaces unexpectedly many generations later.

It also says that magical siblings can be born as in the case of Collin and Denis Creavey, but not always for example Lily and Petunia.

The explanation in the wiki comes, in part, from a 30 July 2007 webchat with JKR.

J.K. Rowling: Muggleborns will have a witch or wizard somewhere on their family tree, in some cases many, many generations back. The gene re-surfaces in some unexpected places.

  • Answers based on the HP wiki alone are generally not accepted. Can you provide a quote from a canon source that backs this up? – DCOPTimDowd Aug 11 '17 at 14:59

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