death to capslock

Absolutely correct. The Creevy brothers could have been halfbloods. All we know for sure is that their father is not a wizard. (Actually, the idea that Mrs Creevy was no longer present by the time Colin was 11 would explain the situation very tidily.)

However, for quite a few years I believed that if a pair of apparent Muggles produced one magical child, the chances of producing another was exponentially higher. I am not altogether sure that this may not still be the case, but at the time I formulated that theory, I had not been given some further information on genetics, much of which may be due to the Human Genome Project which was barely a gleam in a scientist's eye when I was still in school. Information such as the fact that normal DNA appears to include strings and strings of "empty" genes which appear to contain no data, and could potentially be a perfectly reasonable place for harboring inheritable magical traits for the potential use of future generations.

I still flatly dicount Rowling's statements on magical inheritance since she seems to believe in a 'single-gene' theory where all magic is due to the inheritance of a single gene, despite the fact that her own story repeatedly gives us statements about "rare" magical gifts such as parseltongue, or the seer's gift, and the fact that different witches and wizards apparantly have magic of different strengths -- which is all incompatable with the view that all magic is tracable to a single gene. Particularly when you further muddle the issue by postulating non-human magical species which can cross-breed with human wizards and produce offspring which display their non-human parents' specific magical gifts.

Since that time however, I've refined my original theories a bit to postulate the Squib factor as a spontaneous mutation that disables the expression of magic. I am hypothesizing that with the Squib factor present, magic does not build up in and need to be expressed (in the unintentional magical breakthroughs common to juvenile wizards, certainly, but cannot be consiously channeled and projected either). And the Squib factor is a single gene, and it's dominant. If it is present, the offspring is a Squib. But, like all dominant genes, once it fails to be passed on, it's gone. Any magical traits lurking in the DNA are also inheritable, but they operate as recessives. Recessives can continue to propigate for eons and you'll never see them so long as there is a dominant present to supress them. Remove the dominant, and they manifest.

Muggles have no dominant which would supress magical traits. Which explains why, in canon, wizard/Muggle pairings invariably seem to produce wizards. Following this hypothesis, Wizard/Squib pairings are as likely to produce Squibs as wizards. Squib/Muggle pairings may produce wizards *or* Squibs, but never produce plain Muggles. Any Squib offspring are erroneously classified as Muggles. They are, in fact, undocumented Squibs.

Ergo: all "Muggle-born" wizards have at least one Squib parent. Some may have two, although the chances of producing a magical child in such cases drops to 25%, rather than the 50% typical to Squib/Muggle pairings.

Indeed, at a statistical probability of 50%, you would expect for the chances of a magical child to crop up before memory of a grandparent or great-grandparent having come from "somewhere else" to be higher than the indications in canon. But then since the original Squib ancestor probably spent a great deal of effort in concealing his origins, perhaps it's not that remarkable.

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That one or both Creeveys were present when Minerva sent the underage students out from the Great Hall is not a problem. The Creeveys had the DA galleons, so they could know that the battle was coming - and indeed we see DA members starting to arrive at the ROR just before everyone went to the Great Hall. This of course assumes Neville found a way to communicate more than just a time and place of meeting via those coins because the DA members who were outside the castle also needed to know the ROR was accessible via The Hog's Head and that it was indeed the battle, not a minor DA activity.

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Also, for the Creeveys to be able to attend Hogwarts during Voldie's rule it wasn't enough for them to have a magical parent, the magical status of said parent had to be known and provable. Dean suspected his bio-dad may have been magical but with him not being in the picture Dean couldn't claim his status as half-blood. For the Creevey boys to attend school that year they had to have known that their mother was a witch and she should have been able to document her status.

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mary-j-59.livejournal.com

Oh, I love your gene theory! That the Squib gene would be dominant makes sense of the population figures that make no sense at all, otherwise. And I think it's likely the Creevey boys were indeed Halfbloods. But, as Oryx says below, they would have to be able to prove it to be allowed in the school as students. At the moment, my favorite theory is Terri_Testing's fictional one: that a lot of the Muggleborn kids were hiding out in the forbidden forest and that some of them had contacts at the school. Not canon, of course, but it makes some sense of questions like this. ;).

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Ugh, I have spent way too much time trying to figure out wizarding genetics. Have you considered epigenetics as the source of the squib factor, something that causes a magical gene to be switched off and then switched back on several generations later?

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Well, like I say, switching off a single magical gene wouldn't be enough to produce a Squib, because nothing we've seen in canon supports the claim that magic is produced by any single gene. So Squibs are probably not due to any gene being switched off, but by some other factor that interferes with *all* of their magical genes in some manner.

I'm not a geneticist, but that sounds more like something added than something faulty which later corrects. Because the magical traits are still there or there would be no Muggle-born wizards.

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Well, we know that Colin could have come back due to the DA coin that he still had.

I suppose it's possible that Dennis just tagged along, but Minerva forced him to leave because he was underage. Colin may well have been 17 by May, so she couldn't chase him off as well.

But them being found to be halfbloods at some point off-page during Books 3-6, makes as much sense and doesn't require nearly as much back-bending.

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sunnyskywalker

You have me imagining a very interesting phone conversation now, with Milkman Dad calling up his wife after they separated ten years ago. "Hello, Edna, it's Travis. Yes, it's been a long time. Listen, I know this might sound odd, but are you by chance a witch? ...yes, both of them. Would you be willing to put that in writing for the school records?"

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terri-testing.livejournal.com

IWell, if Mrs. Creevey were a Squib who'd been rejected by her family, having children who had the ability for whose lack she'd been rejected might be very painful, no? And her sons, once at Hogwarts, wee being trained to look down on Squibs. She might not choose to mention her own background to them. And if her birth family had abandoned her to the Muggle world and lost track of her completely, her parents and siblings might not realize they'd grandsons/nephews at Hogwarts. The name Creevey certainly would convey nothing to them. The only way someone might guess is if there were a stong family resemblence and someone at Hogwarts to notice it and make the connection.

But her decision not to let her children know her own background and family ("I was orphaned at eight and sent to foster care") would change when the Muggle-born Registration Commission came along.

At that point of course she'd step forward and say, "I, the mother of these two supposed Muggle-borns, am actually the Squib daughter of A and B, Purebloods for three generations. You can see the scorch mark on the family tree right next to the name of my elder brother Corvus."

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Actually, we're told in DH34 that Colin was still under-age.

Then Neville nearly walked into him. He was one half of a pair that was carrying a body in from the grounds. Harry glanced down, and felt another dull blow to his stomach: Colin Creevey, though under-age, must have sneaked back just as Malfoy, Crabbe and Goyle had done. He was tiny in death.

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The battle took place in early May (May 2nd in interview), 8 months after the cut-off date for a cohort. So assuming births are spread evenly through the year, I expect one out of three 6th years to have been underage at the time of the battle.

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I don't think it necessarily would be that difficult to figure out if your long-lost mother had been a witch; it could be as simple as asking the Hogwarts professors if they remembered teaching a girl with your mother's maiden name. Proving that this former student was, indeed, your mother might be trickier, but you might have evidence such as photographs, a marriage certificate or announcement in the DP, a will, wizarding relatives who were willing to vouch for you as family, etc.

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Ah. Okay. He wasn't underage by much. He would have been a 6th year, and due to turn 17 by the end of August.

So, then it probably was Colin that Minerva was trying to shoo away.

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Not just that she was a witch, but one with ancestry and evidence for such to convince Umbridge. We don't see Hogwarts staff testifying for Mary Cattermole.

So there are plenty of scenarios under which Mrs Creevey was a witch and her sons still didn't attend Hogwarts in 1997-8.

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sunnyskywalker

You know, that makes me wonder exactly what was allowed as evidence. Was she claiming that Muggleborns had all "stolen" their magic at age 10 or 11, so that professors' testimony wouldn't count? But you'd think the Hogwarts Quill records would be considered reliable, and the Quill seems to record children pretty young (at birth, even, if Harry isn't unusual in this regard), so what official excuse could be used to suppress or ignore them? That parents steal magic for their infant children somehow?

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I suppose Umbridge had to discredit the quill somehow - maybe she claimed that 'the old Muggle-loving fool' sabotaged it so that it allowed all those magic-thieves in. (No, Rowling didn't show nor tell anything about that, it's yet another plot-hole.)

From what we see at the one trial we are shown Umbridge interrogated people about how they came to be in possession of wands and about their parents. To be considered a true magical person one had to demonstrate at least one line of ancestry that doesn't go back to all Muggles. I don't know how many generations back she would have gone.

I mean, suppose that Severus had not been a DE. His father was a Muggle. He claims his mother was a witch, but if the Princes were a little-known family, or if perhaps Eileen herself was a half-blood and only her mother was of wizarding ancestry - does Severus even know her maiden name? Hypothetically he might have been in trouble.

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Maybe Umbridge believes that Muggle-borns are, in reality, the bastard children of muggle women who "stole" the magic from innocent, unsuspecting wizards.

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Oh, and the fact that these muggle mothers have "stolen" magic from various unsuspecting wizards explains why the legitimate (inbred) children of these wizards then turn out to be less powerful.

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OK, I think I see what you're saying.

But, once you allow for magical ability to be dependent upon more than one gene, I don't think you even need something like spontaneous mutation to explain wizarding genetic patterns.

Let's suppose that magical ability is dependent upon two genes, each with two alleles.

Gene 1 Alleles: U,u U is dominant for magical ability

Gene 2 Alleles: W,w W is dominant for magical ability

There are 16 possible combinations from these two genes. Both U and W are required for magical ability, so a wizard or witch could have the genotypes UUWW, UUWw, UuWW, or UuWw. And a squib or muggle could have the genotypes UUww, Uuww, uuWW, uuWw, and uuww.

So, even though U and W are both dominant for magic, it's still possible for two magical parents to produce a non-magical child and for two non-magical parents to produce a magical child.

If the magical population were to be very diligent about "breeding out" the recessive u and w alleles (by not reproducing with squibs), then, within 9 generations or so, a pureblood witch would have a 98% chance of producing a magical child with a pureblood wizard, a 90% chance of producing a magical child with a Muggle-born wizard, and an 81% chance of producing a magical child with a Muggle.

You can view the math for this here (https://docs.google.com/spreadsheet/pub?key=0Asq6Ul6gdxBCdHVhSlZidVVjV080TEtJWTdxa2VLZ2c&gid=0) (Like I said, I've spent way too much time thinking about this)

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You probably know more about it than I do, but yes, making the issue dependent upon two factors rather than one would explain a lot of the variables. Unless the variables are single-gene additions having little to do with magical ability, but only operative in the presence of active conduction of magical energies.

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Lol, no, I make no claims of expertise when it comes to this stuff. I've been working on the math on and off for months, and I'm not sure if it's even right. I just don't have a life. :p

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sionna-raven.livejournal.com

IMHO Umbridge's committee works more on psychology than on gentic proof. If a Muggleborn hands in his/her family tree traced back to the recognizable Squib, he or she publicly surrenders to the Magic Supremacy doctrine.
I can imagine especially Gryffindor or Hufflepuff Muggleborns refusing to do that.
It makes a whole lot of difference to say "Look at me me I'm a real witch or wizard. I went to Hogwarts and can do magic!" or to say "Look at my birth certificate. Here's the Squib grandfather. I am Halfblood. Muggleborns are imposters."

A Muggleborn who has been sorted into Slytherin doesn't have this problem at all. It's a simple line of logic the Pureblood Slytherins would accept:
Slytherin doesn't allow Muggleborns. The Hat doesn't make mistakes. A witch or wizard with unknown or dodgy descent must have Squib ancestors to be sorted into Slytherin. He or she is without any doubt Halfblood!

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So 'true' Muggleborns are descendants of squibs on both sides, one parent Uuww and the other uuWw. And Hermione really is related to Hector Dagworth-Granger.

But besides the two main genes there must be minor modifier loci - that in themselves can't cause one to be magical, but if one is magical some alleles of these loci cause one's magic to be exceptionally strong. That would explain Albus, Tom and Lily (and probably Severus and maybe Harry too).

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