As far as I remember, JKR never actually addressed what makes a child magical, so I feel free to go with what makes intuitive sense to me.

Personally, I prefer the theory that there are NO "muggle born" magic users. I *believe* that the tendency gets passed along Squib lines until it gets refreshed, either as a result of having two squibs breed or by a sport gene spontaneously showing up as dominant.

Perhaps being conceived and bred in a high-magic environment helps to trigger the trait. Think of it as nourishing a chromosome - the way cells can be given an absolutely perfect medium in a Petrie dish. Still, squibs can appear, even (apparently) in the most reinforced bloodlines.

Neville Longbottom's uncle actually put a small child in do-or-die situations to trigger his magic. And he did it more than once. If anyone tossed my five-year-old off an embankment and into rocky tide, he'd NEVER get a chance to drop the boy out a window! I would bar him from my family At The Very Least. I'd set security so high that "Uncle Algie" would be risking his life to get within a hundred yards of my child.

For such actions to be winked at, if not OFFICIALLY condoned, the fear of bearing a magicless child must be very real. It might well be the worst fear a new parent can feel, right up where we fear cord accidents causing brain damage.

I'd be interested in other people's theories...

 

See the following posts from another thread(read them in order):

http://forums.darklordpotter.net/showpost.php?p=158397&postcount=47
http://forums.darklordpotter.net/showpost.php?p=158500&postcount=48
http://forums.darklordpotter.net/showpost.php?p=158504&postcount=49
http://forums.darklordpotter.net/showpost.php?p=158505&postcount=50
http://forums.darklordpotter.net/showpost.php?p=158507&postcount=51
http://forums.darklordpotter.net/showpost.php?p=158514&postcount=52

JKR has said that magic is genetic. But as you will see if you read my posts in that thread, this is actually impossible.

 

I'd always thought that magic had some effect on the baby within the womb, thus effecting the child's brain or genetic code in some minute way that allowed them to use magic given the correct focus and magical knowledge. Then, when the mother (assuming the child was a female) had a fertilized egg, there is a chance (if she mated with a non-magical male) that the slightly effected genetic code would be transmitted to the child, thus making them magical too. However, sometimes a child of two black haired people can be born blond (I forget what this is called) and similarly even a child born from two magical parents might have this small genetic defect not passed on. Being around magic could help this defect manifest, or create it in the form of muggle born children. And given that areas with lots of magic (such as london, with Diagon alley being an example) there might be an increased chance of this small defect manifesting even in non magical couples.

Sorry about the lack of scientific terms, but my memory is like swiss cheese...

 

Humans are fairly standardized genetically - compared to dogs, we're nearly identical.

But if the ability to use magic is not linked to one's DNA, there are a few other explanations for squibs (other than the Utterly Meaningless term "mutation.") Perhaps a woman could damage her ova or a man can damage his germ plasm by magic use or spell damage. The Gift would skip a generation in that case. Maybe exposure to a certain magical potions ingredient might (very rarely) cause a squib "birth defect" much later in life. Did JKR ever actually address the issue of whether squib births or muggleborn sibs tended to run in families?

Neville HAD the ability, but it only showed up when he had to use it in immediate self-defense. This implies that at least accidental magic is more like an adrenaline burst. Does this mean that the mind could control whether one is or is not able to use magic? The psyche is a frighteningly complex thing: fugue states, hysterical paralysis, PTSD, MPD (for those who believe in it,) are all assumed to be completely involuntary reactions. They are done by the mind, without the conscious making a decision. The thing is, all these conditions are a result of external pressures.

Do the children at Hogwarts set fire to their bedclothes during night terrors? Is there some kind of weak calming charm on the dorm rooms to minimize ...er... sleep-casting? How many young muggleborn children accidently kill themselves by involuntary magic? Perhaps a near-term fetus could do itself lethal damage, leaving a mother to wonder what caused an abortion in what looked like a healthy pregnancy?

 

I think that magic (even in the human body) would have to have some form of sentience, as we do not see any sleep-casting or spells coming from the womb of a pregnant woman. This sentience (maybe attached to the sub-concious) would only come into play in extreme circumstances where there is no possible way out except with super-natural means i.e. magic. Being thrown off a cliff would probably qualify, at least in my mind.

 

Well, since Squib is also a word of a firecracker that doesn't quite go off, I've always thought they had some magical obility. Squibs can see ghosts and Peeves and what-not, they can use magical intruments, and take familiars. They obviously aren't totally without magical ability. Because of this I've always assume that Squibness is a by product of mother drinking to much fire-whiskey or some such rot.

Mudbloods most likely don't exist. When you have a society full of morally corrupt men about to bend women to their will and erase memory, a little bit of harmless rape shouldn'dt be to hard. Wizards might get sloopy and get muggles pregnant from time to time. This would really explain the prejudice against muggle-borns, as you shouldn't want your child marrying a sibling unknowingly. (Was Lily Potter really a Weasley?)

 

Yeah, Apparition + Imperius + Obliviate = A rapist's wet dream.

 

[Arthur Weasley as a rapist]
Considering HOW thoroughly Molly ruled the roost, maybe he wanted some revenge on ... NO! NO I Do Not Believe it!

* with immense dignity *
I'm going to ignore that Utterly Impossible suggestion.

So there!

 

Here's my idle speculation on this:

Rather like the several dozen genes that allow for color vision, e.g., ability to do magic could be the result of a collection of sympathetic genes and not just a single "on/off" gene. Some permit extension of the senses to perceive magic. (The "quintessence" that squibs have and that muggles lack). Others confer, to varying degrees, an ability to tap into and channel magic. Still others can block this access to magic. Some of these genes could have complex interactions with other genes and could express characteristics in muggles unrelated to magic. This would account for their being present in a significant fraction of the nonmagical population. A random muggle could carry several such genes and, through fortuitous combination with genes from another muggle, could lead to muggleborn witches or wizards.

Similarly, through intermarriage, recessive genes that block access to magic could lead to higher frequencies of squibs among children of purebloods than in the mixed blooded. One might wonder what the survival value of squibness is, but given the several wars where wizardkind were targeted as well as various creatures such as vampires and lycanthropes who prey on (and regard as delicacy) wizardkind, one could imagine selection processes over the years that would advantage such genes.

 

The problem with the Genetics approach is that JKR has referred to it as "the magic gene" which implies just one gene controlling it rather than multiple genes, which would be compatible.

 

I agree with Taure that perspicity's thoughts can not stand up to JKR's chatter, but a magic gene can still work. To reiterate what Banner and I have said, if Squibs are not created genetically, but due to improper development of the fetus, there can still be a magic gene. This gene can be either recessive of dominate.

 

OK, then I'll believe that she oversimplified the complex process needed to create a magical baby. It IS genetic - just more than one.

Also, notice how often the kids look like their parents. Draco and Harry both bear a striking resemblance to their fathers, the Weasley/Prewitt lines certainly breed true. I'm pretty sure that JKR stated Hermione resembles her mother. Do we see any other students' parents? Is there a description of Luna's father?

This might be coincidence, or JKR trying to help younger readers keep track of who's who.

 

Does this mean Ginslut will look just like her mother in 15 years...

 

That's a bit oversimplifying it. After all, though Harry is said to look like his father, he is even more often said to have his mother's eyes. Malfoy is also said to look like his mother in GOF. And I don't recall any mention of Hermione ever looking like her mother, or even any description of her mother at all. In the case of Ginny, due to her light build I find it more likely that she'll take after her father: thin and balding.

 

Sooo ... was there ever any mention of whether muggleborn students tended to have sibs who were magical, as well?

 

Not that I can think of, unless the Patils are Muggleborn? Though they're twins not siblings, so I guess that wouldn't count.

But if it were a single recessive gene then every 1 in 4 children born to two parents with the gene would be Muggleborn (statistically speaking).

Edit: Colin and Denis Creevy are Muggleborns and both magical siblings.

 

With Lily and Petunia one is magical, while the other is muggle. Correct me if I'm wrong, but doesn't someone say something about to muggleborns from the same family being rare when Dennis Creevy shows up?

 

That supports the magical gene theory, but doesn't confirm or deny the multiple gene theory. Do we have any indication of the creevey's magical prowess?

 

I'm pretty sure that it was stated flatly that Dudley was unable to see the Dementors, so he isn't a squib. He's a muggle, possibly a carrier of the magical ability. Does anyone remember whether Petunia could see magical creatures or use magical items?

 

Squibs aren't able to see Dementors either.