Huh. Not quite...

[conuly]

Reading JKR's site, she has some new stuff about squibs up (told you that Mrs. Figg never really saw the dementors, and couldn't if she'd been there). Among other things, she says that squibs are so rare because "magic is a dominant and resilient gene".

Well, I'm not going to ask what "resilient gene" means. However, let's take the statement that magic is governed by a single dominant gene at face value.

We know that Dean has brothers and sisters, JKR's site said that somewhere. They're apparently only half-siblings (and presumably on his mother's side), but that doesn't matter to this entry. We also know that his story was cut out of the HP books, his dad (unbeknownst to him) was a wizard. Okay.

Now, Dean's siblings don't go to Hogwarts. That means that Dean's dad only had one Magic gene (M) and another gene that says no-magic (m). His mother presumably has no copies of the magic gene, because she's a muggle (mm).

So, Dean's genes are also Mm. That's the only possible outcome. Now, let's say that Dean gets on with somebody else who has one muggle and one magic parent. That person would also have to have the combination Mm, unless of course there was a random mutation (such as the one which presumably is behind Hermione's existence).

It's not hard to put together a simple chart:

x  M    m

M  MM   Mm

m  Mm   mm

So, Dean's kids would have a 25% chance of not being magical, despite having two wizarding parents.

It's not altogether unlikely that he'd marry a muggle - after all, he grew up with muggles, sees them every time he visits home, is part of that world as well. I'm not making another chart, let's just say that now there'd be a 50% chance of his kids being non-magical.

Of course, you say, there's still the purebloods! Surely squibs are only the non-magical children from pureblood families!

First off, we don't know that. Secondly, that argument doesn't hold water. While it's certainly possible for a family to pass along a recessive gene for generations before it appears, it's not that likely. And we know that there aren't very many pureblood families left. More inbreeding, more chances of squib-gene carriers to meet and have kids, more squibs. You'd expect to see something like a quarter of all children born to wizard parents being squibs.

Well, of course, maybe they are, and people just kinda hush it up, send them out to be adopted, thus making true squibs (nonmagical kids raised in the wizarding world) rare.

But...

Look at Neville. Until recently, he didn't seem to have much magical talent, his family thought he was "all-squib for ages" and that he wasn't quite magical enough to get into Hogwarts. By contrast, some people (Dumbledore, Voldy) seem to be excessively powerful, doing things "with a wand I'd never seen before". It would seem that there's a range of magical ability from muggle/squib to powerfulwizard.

A range of magical ability... hm... kinda like there's a range of skin color from "black" to "burns in moonlight" or a range of heights from "dwarf" to "giant"? But these things are multi-gene traits. They're not governed by a single recessive gene (and, to an extent, they are also influenced by environment. Tallness is a recessive trait (found in many genes), but your height can be affected by your diet in childhood and whether or not you slept with a nightlight). It seems logical that magic is similarly governed by multiple genes. Hermione's parents might be partly magical without knowing it - not enough to get into Hogwarts, but enough to pass on the right combination of genes to their daughter.

But this only works for multi-gened-traits.

Comments

Re: I have. *looks sheepish*

[marveen.livejournal.com]

What pointed ears?

(Jackson threw THAT in to be confusing. Tolkien described them thus: "I suppose hobbits need some description nowadays, since they have become rare and shy of the Big People, as they call us. They are (or were) a little people, about half our height, and smaller than the bearded Dwarves. Hobbits have no beards. There is little or no magic about them, except the ordinary everyday sort which allows them to disappear quietly and quickly when large stupid folk like you and me come blundering along, making a noise like elephants which they can hear a mile off. They are inclined to be fat in the stomach; they dress in bright colours (chiefly green and yellow); wear no shoes, because their feet grow naturally leathery soles and thick warm brown hair like the stuff on their heads (which is curly); have long clever brown fingers, good-natured faces, and laugh deep fruity laughs (especially after dinner, which they have twice a day when they can get it). Now you know enough to go on with.")

Re: I have. *looks sheepish*

[adiva_calandia]

True. I am justly chastised.