In the original post, I talked about magic being a recessive gene, which is true, but I did talked about the topic as if there was only a "magic" and a "not-magic" gene, or a rather basic discontinuous monohybrid cross, or there is no 0-100% magic, and there is no other genes that can influence magic.
Which was rather like this.
I'm not going to get into the details of genetic science for you, at least not until the complex stuff.
"But wait!" You cry, remembering the first Blood Purity post. "Voldemort's parents were a witch and a Muggle!"
Yes, yes indeed. This means that for Tom Riddle Jr. to be magical, his father either had to be an "Mm" guy himself, or the magical inheritance is more complicated than this. While it is possible for Tom Riddle Sr. to be descended from a Squib, we are going to explore the possibilities of if he isn't, instead he's solid Muggle, "MM".
I'm not going to make another square, but if magic worked like the above square, Merope Gaunt and Tom Riddle Sr. children would all be unmagical, but would also all carry the magical gene. We all know that Voldemort isn't a Muggle, obviously, so how would magical inheritance have to work instead?
Technically, it could still work like this, with an "mM" or "Mm" being a Muggleborn, but not only would that mean far, far more witches and wizards than obviously exist (re: the 40 to 50 student graduating class at Hogwarts versus the many thousand Muggle graduating class in Britain), but also that Muggleborns have less magic than Pureblood "mm" witches and wizards, which I've already established isn't a thing, at least on a diagram like this.
If you need a recap, just remember that Harry, Hermione, and Voldie would all have less magic if that was the way it worked, yet clearly, they all three are very powerful.
We also should know its more complex than that anyways, since Neville is a weak wizard while Dumbledore is a very strong one, but both are Purebloods.
One way to account for differences in magical power is with a system similar to how blood types are inherited.
Blood Types have three alleles, an Ia, Ib, and i, for A-type, B-type, and O-type, respectively.
Magic could work like Ma, Mb, and m.
This is still a discontinuous monohybrid cross, as in there's a 100%, a 75%, a 50%, and a 0% and it's still one gene.
Rather like this.
Perhaps an "Mam" is someone like Voldemort, who inherited one full-Muggle and one full-witch, making him a Half-Blood, but, maybe a strong one, while "Mbm" would be someone like Neville who is still a wizard but a weak one - rather like Ron or Seamus Finnigan.
The issue here is what "MbMb" would be. And where would the parents of Muggleborn's go? Or Squibs? To pass on the gene, they'd have to magical themselves, and then Muggleborns wouldn't exist, since they would have to have a magical parents. Half-Bloods could exist, and would explain why they seem to be stronger, rather a pure Muggle with a pure wizard makes an "Mam", but in the case of a Muggle who carries "Mb" would lead to weak Half-Bloods, that so happen to be minor characters.
One idea for the "MbMb" is just a different kind of Muggle, but there still isn't a place for Squibs or Magic-carrying people.
A different idea on the magical inheritance thing is a dihybrid cross.
A Dihybrid Cross involves two different genes that affect one sort of thing. The internet examples like to use, say...
| A | White Hair |
| a | Black Hair |
| B | Coarse Hair |
| b | Fine Hair |
...but in this case...
| N | Non-Magic |
| n | Magic |
| W | Weak Magic |
| w | Strong Magic |
Look, another chart! It's almost like they're cool or something.
Anyways, "NN" or "Nn" means that they are non-magical. "nn" means they have magic. Easy, right?
"WW" means that if they have magic, it's weak magic. "Ww" means if they have magic, it's average power magic. "ww" means if they have magic, it's strong magic. Rather, magic power uses incomplete dominance, in this case.
You can get some interesting combinations out of this as well. Say that a non-magical who carries the "ww" combination for strong magic can be/is a gypsy or a fortune teller or one of those medium that connect to ghosts. A "Ww" combination on a non-magical might mean you would be naturally more empathetic or better with animals or plants or that you have some natural talent in something.
Would that mean that I carry the strong magic gene for natural talent at over-analyzing?
The good thing about this chart is that it becomes very easy for there to be Squibs and magic-carriers. In fact, I marked the chart for you. A red dot means non-magical, a purple dot means a magic-carrier - like Squibs or those mysterious parents of Hermione or Lily we never learn about -, a green dot means weak magic, and a blue dot means a strong magic carrier.
Look, I'll make another table for you, because I love you.
In a minute, because there is empty space here.
I like this idea far better than either the second one or the first one, back on the original page. The reason for this is that it accounts for natural skill levels between, say, Draco, who grew up with magic and likewise knew spells that weren't part of the curriculum, and his (probably) second cousin Harry Potter who didn't grow up with magic, was an average student, yet could scare of a horde of Dementors by 14 or defeat one of the strongest wizards in Britain by 18.
Also, here's that table.
| NNWW | Weak Non-Magical | People with poor immune systems or blood diseases? |
| NNWw | Average Non-Magical | Average Joe, Vernon and Dudley Dursley |
| NnWW | Weak Non-Magical Carrier | Probably not nearly as weak as NNWW, Filch? |
| NnWw | Average Non-Magical Carrier | empathetics?, vets, florists; Petunia Dursley? |
| NNww | Strong Non-Magical | mystics, gypsies, mediums |
| Nnww | Strong Non-Magical Carrier | Same as NNww, some Squibs, Hermione's parents, naturally talented? |
| nnWW | Weak Magical | Ministry Workers |
| nnWw | Average Magical | Ministry Workers, Minister, some Aurors |
| nnww | Strong Magical | Voldemort, Harry, Dumbledore, Hermione, good Seers, some Aurors |
There are, of course, other ways magic could be inherited, like with multiple genes, as it it is with hair color or height, and that's probably how it is, but the dihybrid cross is fairly close to how multiple genes would work in reality.
As for where the Squibs get a non-magic gene if they are supposed entirely pureblood? It's very likely that there is a Muggle somewhere in the line, but that means that the Muggle gene carried, right? And if you carry a non-magic gene, you must be non-magic, right? So that would mean that Squibs can't technically exist, unless magic is dominant or co-dominant, or, well, magic explain why Squibs exist.
That's the easy way out, but it is amusing to answer aimless questions like that. Magic. Hah!
So if magic was dominant, the numbers wouldn't work out at all, which is my primary reason for making it recessive in the first place. Numbers almost always suggest whether genes are dominant or recessive, but in the case that it is actually dominant and some form of complex circumstance leads magic to be just uncommon - this is supported by how Colin and Dennis Creevy are both Muggleborns, but also brothers, and are very unlikely to both be magic according to the above chart - I will humor you with even more delectable tables.
| NNWW | Weak Magical |
| NNWw | Average Magical |
| NnWW | Weak Magical Carrier |
| NnWw | Average Magical Carrier |
| NNww | Strong Magical |
| Nnww | Strong Magical Carrier |
| nnWW | Weak Non-Magical |
| nnWw | Average Non-Magical |
| nnww | Strong Non-Magical |
It's virtually identical to the previous one, but flipped, where most people are magical, and where wizards can "carry" Muggle, which would sort of put Voldemort's agenda into a new perspective, since he wants to kill a sort of byproduct of magic, or that being non-magical is a disease, of a sort. It still makes sense, except, again, for where do Muggleborns come from? If they are descended from Squibs, they must get a magic gene, somewhere, and since Muggle's can't carry magic by this table, it's a bust as well.
What about co-dominance?
Co-dominance is where two genes that are both Dominance will give and take if someone happens to have both of them. Incomplete dominance is similar, but they combine and share, in this case. An example of this is if a hamster has a black hair gene and a white hair gene, and they are both dominant, then that hamster would have white and black fur, likely in splotches, according to co-dominance, and grey fur according to incomplete dominance.
If magic worked that way..., and, back to where magic is recessive.
| NNWW | Weak Non-Magical |
| NNWw | Average Non-Magical |
| NnWW | Muggleborn Parents (Weak Co/In Dominance) |
| NnWw | Squibs (Average Co/In Dominance) |
| NNww | Strong Non-Magical |
| Nnww | Strong Magical Carrier (Strong Co/In Dominance) |
| nnWW | Weak Magical |
| nnWw | Average Magical |
| nnww | Strong Magical |
I'm under the assumption that if a non-magic and a magic gene collide, then the result is a Squib or a magic carrier. But due to how obviously un-magical Squibs are, there has to be something that is magical about them.
For one, they seem to be able to see magical places, since Filch works at Hogwarts, as a Squib. Perhaps Squibs themselves have a strong connection to animals, or at least cats, because both Filch and Arabella Figg have cats, and Filch talks to his cat, who can seemingly understand him.
Other theories are that they might have some sort of magical resistance or maybe they do have magic but they just can't use it, which explains the seeing-magic thing.
In other words, magic would share an incomplete dominance with non-magic, resulting in the inability to use the magic they have.
I put Squibs as magically average-ish, since there isn't indication of Squib descendants being able to see the likely obviously magical places, and also because it's more believable to say that the closer related you are to a magic family, the stronger you are magically. As for the "Strong Magical Carrier", if someone inherits enough magic, magic would probably show over the non-magic-ness allowing access to magic, but resulting in a weak witch or wizard, which would likely have a Squib as a kid.
So yeah.
Complicated.
The way magic inheritance probably works is actually similar to how canon likely shows it, rather, with, well, a bunch of gene combinations that determine magic, rather than the still singular one I've been dealing with the rest of this post.
Let's say that there is... six genes that determine whether someone does or does not have magic, still an M and an m.
| MMMMMM (6 Large M's) | 100% Non-Magical |
| MMMMMm (5 Large/1 Small M's) | - |
| MMMMmm (4 Large/2 Small M's) | - |
| MMMmmm (3 Large and Small M's) | Squibs and Similar, most likely |
| MMmmmm (2 Large/4 Small M's) | Weak Magical/Commonly Muggleborns |
| Mmmmmm (1 Large/ 5 Small M's) | Average Magical |
| mmmmmm (6 Small M's) | 100% Magical; Strong Magical; Often Pureblood and some Half-bloods |
This table, is, of course, not that complex, but I'll explain it anyways. A "typical" Muggle would likely have no, one, or two Magic genes, but more inclined towards none or a single gene. If say a fully magical person and a fully non-magical person had children, more likely, those children would be non-magical themselves, as being non-magical is still dominant, or rather, they'd be the same in strength as a Squib.
If someone's grandparents and parents were all magical, that is generally enough pure magic for that someone to be considered a pureblood, even if they aren't, technically. While this isn't directly stated, because there aren't "three-quarters bloods" just hanging around, and because there are pureblood families that aren't very "pureblood-y" - i.e. Ancient and Noble - like Crabbe and Goyle, most likely, there is reasonable support for this statement. This obviously doesn't apply to Squibs.
Of course, that's not something anyone can tell just by looking at you, but the strength of their magic is a strong indicator towards how much magical blood they have, like how Hermione is probably the same magical strength as an ideal pureblood, as is Voldemort and Harry (re: the third year Patronus, anyone?). It's very likely that those who knew often forgot about Voldemort's blood status, which makes him widely considered a pureblood, especially considering his hatred for Muggles. Snape is similar in that regard, because, remember, he joined them freely before becoming a spy.
Still skirting around the whole Snape thing.
While in this table-example, for a "Pureblood" family to have a non-magical kid, they'd have to have enough Non-Magical genes for that to work. Now, in the case of people like Dolores Umbridge who has a Squib brother, Muggle father, and full witch mother (it's on Pottermore), that non-magic that appeared in her brother is easy to find in her father.
Her mother would presumably be "mmmmmm" and her father with only one (MMMMMm) or two (MMMMmm) magical genes, enough to make Dolores Umbridge a weak witch magically and a Squib/Non-Magical brother.
While the Squibs we all know in the story - Figg and Filch don't seem to come from any notable wizarding families, Squibs would inevitably end up as an offspring to some higher status families, like someone with a mental disorder in Muggles. It likely works the same as well, with just 3 genes out of the 12 between two people being non-magical, and thus capable of a non-magical child. More likely, the total gene count that determines magic is more than 6, possibly even as much as 2- or 300, requiring maybe 150 to 250 of those genes being magical to inherit magic.
Since magic would be recessive.
This is more likely (being way more genes), since there is a scale to strength, there isn't, say, 50%, 75%, and 100% magic, that's too definitive.
If there is upwards 200 magic-determining genes, at, say, 100, you'd be a Squib, and 101 would be an extremely weak magical, so weak they likely wouldn't even go to Hogwarts, or a "1% Magical" with 200 genes being magic and 0 genes being non-magic, that would be Merlin-strength, or a "100% magical".
But doesn't this mean the Purebloods are right? That interbreeding with Muggles really is making them weaker?
Perhaps. I didn't even know this would be the result when I started writing it, not until I wrote the paragraph 2 up from here did I see where I was going.
Yes, though, it isn't right to be derogatory and prejudiced about the more-likely-to-be-weaker Muggleborns, so Draco isn't suddenly the man with all the answers or anything, but no one just makes up all the Pureblood vs. Half-blood vs. Muggleborn thing for it to become immensely widespread supposedly everywhere if the TriWizard Tournament Year is any indication if the idea didn't make sense. I know that's a bit of stretch for the trust in people's judgement, but we believe that Napoleon was short today because Napolean was 5' 6" which is short today, but he wasn't when he was alive.
It makes sense, but it might not be fully true, keep that in mind.
But this is all just a theory.
Shiizumi Valé, otherwise WillowEye10329 on Pottermore, giving you a lovely dose of over-analyzing. Signing off.
