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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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  • Parents of a Muggle-born Witch/Wizard aren't necessarily Squibs. If a person's biological parents are non-magical and they are themselves non-magical, they are a Muggle. If at least one of a person's biological parents are magical and they are not, they are a Squib. – DisturbedNeo Apr 20 '17 at 12:03
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    In addition, if you assume the "Magic" trait to have mutated from early humans, then it's possible there are people in the world who's ancestry has never had the ability to cast magic and never will, unless that trait mutates in one of their children. Likewise, it's possible for an early spellcaster to have had non-magical descendants all the way down to the 21st century, where one child suddenly had the trait activated and they're the only magical descendant in a long line of Muggles. – DisturbedNeo Apr 20 '17 at 12:06
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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
  • @xDaizu Indeed. But the scientist in me needs an explanation. – Zommuter Apr 20 '17 at 12:39
  • I'm confused by your last sentence; what about "Muggle-borns will have a witch or wizard somewhere on their family tree" doesn't imply that "Muggle-parents of Wizards/Witches are actually Squib(-descendant)s"? It seems to me like those are saying exactly the same thing. Or did you mean to quote Rowling when she said that magic was a dominant gene? – Jason Baker Apr 20 '17 at 13:25
  • @JasonBaker To me the second quote implies that the descendant of a Wizard can only be another Wizard or a Squib, but never a Muggle. The first quote does then however indicate that a muggle-born Wizard's parents are actually not pure Muggle but rather partially Squibs. But the family trees of the few known Squibs don't provide any information what Squibs' children could actually be... – Zommuter Apr 20 '17 at 13:35
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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
  • @ibid If you can hunt down an actual copy of that, I'll accept quotes therefrom as answer ;) – Zommuter Apr 20 '17 at 14:28
  • @ibid I heard about that, my (jesting) point was that you'd need to actually obtain said publication in order to quote from it. The title alone doesn't state anything about cross-breeding (Martian mushrooms and the likes) – Zommuter Apr 20 '17 at 14:32
  • related post....: https://scifi.stackexchange.com/questions/18783/where-did-the-magic-blood-of-the-harry-potter-universe-originate-from?rq=1 – DVK-on-Ahch-To Apr 20 '17 at 14:37
  • @Zommuter - Will a picture of said publication suffice? – ibid Apr 20 '17 at 14:38
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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
  • It is known that most of the Parseltongue people are from Slytherin and as mentioned in the last book, Tom Riddle's mother side was from that ancestry line. They were also fluent in Parseltongue. This shows the magical abilities can be inherited from the ancestors. – burcu Aug 11 '17 at 13:31
  • ....how is this question not asking for real-world explanation and ie - not off-topic? The author of the series gave an in-universe answer. Regarding the second half of your question - see these existing questions: https://scifi.stackexchange.com/questions/119770/can-muggles-give-birth-to-a-magic-sensitive-child-similar-to-a-squib https://scifi.stackexchange.com/questions/9254/is-it-genetically-possible-for-a-squib-to-produce-magical-offspring – NKCampbell Aug 11 '17 at 14:43
  • it's not an answer, since it's from a Fanwork, but Harry Potter and the Methods of Rationality had Harry and Draco looking into this issue with an eye to if it also explained the difference in power levels / loss of power over the ages. Might be of interest. (One slightly addressed issue (Harry doesn't mention as it just muddies the waters in terms of explaining things, but he contemplates it) is that Wizard power, like Eye color, may not be dependent on just one gene; multiple genes being involved can screw with the simple Mendelian model most people are expecting.) – K-H-W Aug 11 '17 at 14:52

1 Answers1

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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.

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  • 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