Purple Orchids and Muggleborn Wizards: A Theory of Wizard Genetics

Discussion of the editorial Purple Orchids and Muggleborn Wizards: A Theory of Wizard Genetics (www.mugglenet.com/editorials/editorials/edit-tbrightwater01.shtml) by T Brightwater.

omg thats so confusing and i dont get it at all! but it's well written.

I don't mean to be rude but you all have way too much time on your hands.

Wow! That really was amazingly well thought out and written. It must have taken a while!

As in the case of the sickle-cell gene, there is a trade-off; if these anomalous abilities do depend on Muggle genes, the price paid for the presence of these abilities is the occasional occurrence of Squibs. However, if Squibs marry into the Muggle population, they may contribute magical genes to their offspring, and magical ability may resurface generations later in their descendants, perhaps combined with advantageous genetic factors from the Muggle gene pool.

It's totally fascinating! I'm very impressed!:D

would i be right in thinking that Parseltongue would be in the same category as being a Metamorphagus, in that it's a rare genetic condition of some sort?

I don't mean to be rude but you all have way too much time on your hands.

That was kind of rude! If you don't think that topic is worth your time, then just don't read the editorial or waste more of your precious time posting rudenesses.

I don't really see the relevance of the whole genetics discussion either, but hey, that's what obsessive fans do! :D And really, it was well presented and thought through. And with a small effort at concentration, I don't think it's very hard to understand at all. Well done! :clap:

On the other hand, it could just be magic. :o)

Maybe the magic, like the wand, chooses the person to belong to.

If it is genetics, I agree that simply having magic be a recessive gene (so that the trait can seem to skip generations due to heterozygous pairings) would not explain how a squib could come from an all-magical family, though it could possibly explain seemingly "muggle-born" witches and wizards. And when magic generally does run in families, it is hard to imagine another explanation than "something to do with genetics." But since I'm determined to rain on everybody else's parade, let me be the first to suggest that there may be another reason for this that we aren't meant to know.

a question to the writer: does this theory explain the fact that squibs are more rare then muggleborns? it's said so clearly in CoS, and i wonder.

I am sure that the secret of wizarding genetics, though very interesting to some people (like me) is probably irrelevant to the plotline of Harry Potter.

To T. Brightwater:
What fools these mortals be! Don't listen to dismissals and complaints. Your essay was brilliant, and yet another example of how the Potterverse can explain or introduce us to so many concepts. I hope Jo sees it.

You are persuasive and humorous too. Many thanks.

"Pure-bloodedness" is an issue for many of Jo's characters, in one way or another, so why shouldn't a discussion of genetics be relevant?

Languish wrote:
"would i be right in thinking that Parseltongue would be in the same category as being a Metamorphagus, in that it's a rare genetic condition of some sort?"

Hmm, good point, since it seems to be hereditary in Slytherin's descendants. It must be dominant, since the Gaunts could all speak it and so could the half-blood Tom Riddle (if it were recessive it wouldn't have expressed itself in a first generation hybrid.) This suggests that if Slytherin's descendants had "bred out" more into the general Wizard population, Parseltongue would be a much more common ability.

Mad Hatter wrote:
"a question to the writer: does this theory explain the fact that squibs are more rare then muggleborns? it's said so clearly in CoS, and i wonder."

I think it does; Squibs need to have two recessive alleles of the same gene, while Muggleborns need only one dominant allele of each gene. There is no Wizard x Wizard cross that would produce all Squib offspring, but there is at least one Muggle x Muggle cross (AAbb x aaBB) that would produce all Wizard offspring. (I know it's a small sample, but perhaps the Creevey brothers' parents are such a couple?)

Also, even though Squibs are supposed to be really rare, we know of three: Filch, Mrs. Figg, and Mrs. Weasley's second cousin.

FishEByrd wrote:
"let me be the first to suggest that there may be another reason for this that we aren't meant to know."

Yes, it's quite possible that it's "just magic" and Jo didn't have any particular genetic theory in mind, but it so happens that there is a genetic mechanism which explains the "facts," follows the Mendelian rules and occurs in the real world. If anyone finds it interesting, fine; if not, that's okay too.

PS Thanks, Aloysius!

I don't undestand most of the genetic stuff, but I think I got the general idea. But what about Sirius and James (Pureblooded, in Sirius' case extremely so, and able to become Animagi at 15), or the entire Black family, for that matter?

Thus, Lord Voldemort is not only evil, he's wrong.

ROFL! :rotfl:

Great editorial!

I don't undestand most of the genetic stuff, but I think I got the general idea. But what about Sirius and James (Pureblooded, in Sirius' case extremely so, and able to become Animagi at 15), or the entire Black family, for that matter?

JKR has said, either in interview or in the books, that most "Pure-blood" families aren't really pure. If wizards hadn't mixed with muggles, they'd have all died out by now.

So, really, the odds are slim that there are pure-blood wizards with AABB. Rather, they are more likely to have one or two recessives alleles in there.

Thank you for this editorial. As a high school Bio/Chem student and a prospective Biology major in college, it's always cool to see two of my favorite things (Harry Potter and genetics...I'm such a nerd...) combined.

Since you wrote this editorial (as opposed to earlier ones, which suppose that the genes are Mendelian), surely you know that genetics are often far, far more complex than Mendel said they are, especially in complex organisms for humans. Eye color alone is controlled by three seperate genes, and hair color has at least two genes. I always figured the gene for Magicness (if there is one) would be incredibly complex.

JKR has said, either in interview or in the books, that most "Pure-blood" families aren't really pure.
Most, maybe, but the Blacks? They blasted off anyone who had anything to do with Muggles, so they only way Sirius could have Muggle blood is if a female ancestor had an illegitimate child with a Muggle and passed it off as her Pureblood husband's child. Not impossible, but fairly unlikely. The Blacks were like the Gaunts, they pretty much married cousins rather then dying out. That made then rather insane (although probably to a lesser degree then the Gaunts), but it's hard to argue that they're not magically powerful.

I don't undestand most of the genetic stuff, but I think I got the general idea. But what about Sirius and James (Pureblooded, in Sirius' case extremely so, and able to become Animagi at 15), or the entire Black family, for that matter?

I'm not claiming that pure-bloods are always inferior to Muggle-borns; obviously there are many talented and powerful pure-bloods as well. All I'm saying is that pure-bloods don't have an automatic advantage.

Also, Alhara, you're quite right. A two-gene model is the very simplest one I could make work. I believe there are even genes which suppress other genes, which complicate the possibilities even more.

I love your editorial. Ever since we studied genetics in biology I had been wondering about how it would work. It was one of those things that just kept nagging at me. Now I can think about something else. YAY!! Thank You!!

Wow, I really enjoyed reading this! I've been thinking about thi same thing for quite some time, but as I'm not much of a biology person, I just couldn't quite get it. Thanks for helping me out!

Wow, now that's a totally new way of looking at the whole genetic theory thing. Good job on that article! :clap: It IS a little confusing to understand at first, I'll admit (all the letters confused me for a while) but it was still a good explanation. I've always wondered how the genetics of magic worked ever since we did that topic in Biology. I tried to figure something out but it didn't work because Mendelian genetics (which is the only kind of inheritence we were taught) didn't seem to explain the whole thing satisfactorily enough. Glad we've got another concept to fill in the loopholes somewhat.

Of course, like you pointed out, Brightwater, there are so many things in genetics that complicates everything else. Genetics isn't just one simple thing to understand. Scientists are still working out some stuff about it even till today!

Haha. To add on to your 'genes suppressing other genes' point, it could be possible that the Magic gene suppresses the Muggle gene!

I wonder if one day JKR will sort out this mess of genetics for us... but I doubt it, since I don't think she really thought so specifically about the Magic gene's inheritence when she planned out the story and world of Harry Potter. Plus, it's her job to write the story, not fiddle around with how the genetics work.

I suppose if we really can't come up with a theory to explain all the genetics and occurances in the Wizarding World, we can simply say...

"It must be magic." :p

That was a very good editorial! I wanted to try to find an explanation to this myself, but couldn't really find the time...
Anyway, it was very well written and I think it explains everything in a very logical way.

Excellent Editorial! It's very well thought of and very logically explained.
I also think that since muggles tend to marry muggles, and vice versa with wizards, the genes don't mix too much, which adds to the rarity of squibs and muggleborn witches or wizards.

While I think your theory is interesting, the occurrence of Squibs is far, far too high for only two alleles to be at play - after all, as Ron Weasley tells us, most "Pure-blood" families have some Muggle blood, but Squibs are very rare. We only know of three in canon, Filch, Figg, and the unknown accountant Weasley cousin, and if it were true that nearly 7/16 of mixed-blood progeny would be squibs, the Magical world would be simply swimming in them.

I don't know much about genetics (though I'd pondered multiple alleles being in play before) - is it possible for more than two genes to determine a very rare trait? What if the necessary combination took four, or five, or six alleles (I have no idea if this is possible - just throwing it out there). Then, the chances of squibs being produced would be much, much lower.

So too would be Muggle-borns, you say, and there are plenty of Muggle-borns in canon. But! Muggle-borns arise from the entire gene pool, wizard and Muggle, and so the relatively high number of Muggle-borns in the Wizarding world actually arise from a tiny, tiny percentage of Muggle marriages. Meanwhile, Squibs would still be suitably rare.

Does this make sense?

Tabari-- she didn't say 7/16 of all pure-blood marriages with mixed alleles. That was just one kind of pairing. Pure-bloods are probably mostly AABB or AaBB or AABb. Squibs are suitably rare and muggle-borns are suitably common.
However, as much as I'd like to accept this editorial, I think JKR said in an interview that a child is either magic or not. The relative power might be a complex thing but the magic/not magic gene seems to be Mendelian, because if a child is either magic or not magic, that rules out all forms of incomplete dominance. There might be multiple alleles that surpress one another, but there is no "sort of magical" or "really magical", and I think your argument for strength in heterozygous wizards is untrue. Power is a different thing entirely. Voldemort never said only the powerful wizards should marry one another.
While a doctrine based only on the phenotype of the marrying wizards and their ancestors (and pure-bloodedness can be faked by either the wizards or the ancestors, whatever Justin Finch-Fletchy says) is bound to be at least partly wrong, it is possible for the magic gene to at least get buried for awhile if too many wizards marry muggles. It wouldn't die, because it would come up again in the muggle-borns, but that is exactly what Voldemort doesn't want-- a world in which wizards can pop up anywhere but are never guaranteed. Wizards are not quite an endangered species, but some wizards believe it would be just as bad if the wizard and muggle communities were forced back together by their descendents. They never forgot why all those muggle secrecy acts of the 1700s were put in place: witch hunts. Competent wizards are not afraid of muggles for their genes, but for their sheer numbers and blind rage against magic. If heterozygous genetic makeups became the norm, the pureblood wizards, who do not associate with muggleborns who could have told them that the fundamentalist Christians are far less common today, believe an all out war would create such a massive bloodshed that no one would have time to worry about dying out.

No. She said that offspring from two AaBb parents would have 7/16 squib children. However, Seamus Finnigan, for instance, is almost certainly AaBb, as is Dean Thomas; certainly, there must be witches who are AaBb also, and I doubt they're uncommon - if two boys in Gryffindor in the same year are of that genotype. Squibs, however, are incredibly uncommon, and that's where I think the two-allele argument falls apart. Moreover, if the likelihood of having squib children rose proportionally with interbreeding with Muggles or Muggle-borns (those who would carry non-magical alleles), the Pure-bloods would have a much better argument against interbreeding - and by now, I think we'd have heard of that.

I again propose that more than two alleles would have to be in play, that's all.

I really did not understand alot of it and the ones who claim to have understood, I think are mostly lying, sorry but it was rather confusing. I skipped a few paragraphs but I dont understand this whole, 'Voldemort not evil, he wrong', wot u on about?

We only know of three in canon, Filch, Figg, and the unknown accountant Weasley cousin, and if it were true that nearly 7/16 of mixed-blood progeny would be squibs, the Magical world would be simply swimming in them.

...

So too would be Muggle-borns, you say, and there are plenty of Muggle-borns in canon. But! Muggle-borns arise from the entire gene pool, wizard and Muggle, and so the relatively high number of Muggle-borns in the Wizarding world actually arise from a tiny, tiny percentage of Muggle marriages. Meanwhile, Squibs would still be suitably rare.


We know of all muggleborns cause they all go to Hogwards - we don't know a lot of Squibs cause they stay at home. Maybe the Squibs are the same rate as the muggleborns, we just haven't met them.


I really did not understand alot of it and the ones who claim to have understood, I think are mostly lying, sorry but it was rather confusing. I skipped a few paragraphs but I dont understand this whole, 'Voldemort not evil, he wrong', wot u on about?

Why would we lie about something like this? It's no wonder you got confused if you skipped paragraphs. About Vodermort being wrong - she refers to Voldermort praising the pure-bloods. Take some time and read it again, do the gene-crossings yourself and you'll get it :)

We know Squibs are rarer because Ron says so, and he was telling us this fact not just as Ron, but as Ron-the-dispenser-of-information-Harry-does-not-know.

My theory is that the magic gene (or genes) is a mutation. Your editorial here is the best one I have read that contradicts this theory. I understand your reasoning and agree that it does provide an adequite explanation for both muggle born witches and wizards as well as squibs. I now think that magic is not a mutation but is an inheritable genetic trait. I beleive your theory may indeed be correct.

I think there was an editorial already about genetics and Harry Potter. They're very alike. How does this make a difference, though?

I was wondering the same thing a while ago (how there was both squibs and muggleborns) but you do have to remember that the fact that we are talking about magic (something beyond the explanation of science) therefore it wouldn't be too off the wall to think there are an elevated amount of mutations with with Magical people. I do applaud you for going to great lengths to explain this world, but I do think you are reading too much into it. Anyway, very good article.

Tabari- Remember that just because there are two alleles (4 between the two different genes) does not mean that they are found in equal proportions in the population. "A" could be relatively rare in the muggle population, but found more frequently in the magical population. Another possiblility is more than two alleles for the magic trait.

T Brightwater- I loved this editorial...as a biology teacher (and a former human geneticist) I plan on printing your editorial for my students to read.

i really don't know how jkr can say only genes are responsible for magical inheritance, these days everyone knows something about genes but there are a variety of other effects between genes like incomplete-dominance(which is well illustrated in this article), co-dominance, epistasis,supplementary & complementary genes. I did think of writing about it, but it would turn out to be pretty boring and desperate, i think its better to presume that magic is a little genetics and a lot of miracles

Out of all the genetic theories about the Potterverse, I think that this one is the most plausible. Since there is no way to actually test any of the genetic theories that people put forward, the simplest explanation that accounts for what we see in the books, is probably the best. Occam's razor, right?

good editorial. i think that your knowledge of genetics is great, which is key -- i hate when people who don't understand it try to explain it. i hadn't thought of two genes -- interesting. it doesn't sound perfect, of course, because of probability (i think the probabilities of Squibs and Muggleborns are lower than what you suggest)... but it is a good start.

One problem -- why do you so adamantly assume that Merope wasn't powerful? she was meek and weak-willed, but there is absolutely no evidence for her being magically weak. she kept Tom Riddle Sr. under a very powerful love spell for years -- that alone is a testament to her powers.

great editorial.

To T Brightwater: This is an amazingly well thought out essay. Great job. I don't usually read the discussions because most of what people say (particularly the criticisms, such as, "you have way too much time on your hands," or stupid comments such as, "i don't really get it, but good job,") are inane and worthless. But I want you to know that I really enjoyed your editorial. I felt like i learned something worthwhile about real-world genetics, and it was fun because it was put in terms of Harry Potter. So thank you for the education!! :)

A really good editorial. Especially with this recent burst of genetic influenced HP theories. It really explains a lot.
I'm also one of the "nerds" that is really interested in genetics/biology, so I was able to follow your essay without a single problem.
Anyway, good job!!!

This was an excellent piece of writing! I was interested in genetics a very long time ago, and the editorial brought some of the more complex (to me) aspects back to memory. It truly is like figuring out a puzzle -- very enjoyable. Thanks for taking the time to work through this and share your results!

Can anybody give the quote that says Ted Tonks was a Muggle-born? I was sure he was a Muggle, but I haven't my book with me to check...

For all you biology people out there - more than two alleles don't seem to work (after spending an hour with pencil and paper) - but what if magic is a polygenic trait? What if, like the genes that control melanin (skin color), it took two, or three, genes to produce a magical individual?

I don't know enough about biology, frankly, but I'm just throwing the question out there. Also, allele frequency? Perhaps, still going with the original editorial, the Aa allele pair is much rarer than the Bb allele pair, and so a lot of Muggles are BbBb, or bbbb? Oh, eek, except that would increase the rate of squibs, and that's what I'm trying to get around.

I doubt that JK put 1/16th the amount of thought into this as you have (having stated herself somewhere that math and science were never her strong points). But it's entertaining for some of us to discuss some of the more obscure points of the series while we're waiting for book seven.

I liked the scientific explanations in this editorial but I still believe (as I stated in a reply to the LAST genetics editorial) that something MAGICAL happens to the genetics of Muggleborns and, I suppose, Squibs.

I agree with Sayre that Merope's magical problems were probably a result of her environment, like Neville's. I would like to again state that you are either magic or not magic, so a heterozygous genotype for the magic gene, which cannot have incomplete dominance, does not necessarily have anything to do with the genotype or phenotype for what I'm calling the "strength of magic" gene, which might very well have incomplete dominance, as wizards come with varying degrees of power. Most likely, muggles have the strength of magic gene, but it doesn't do anything to them, so it has the same chance as a magical person's to produce a powerful wizard.
It says on page 50, American Version, of OotP (The advance guard chapter) that Ted Tonks is muggle-born.
Is polygenic the type of gene that controls blood type? If so, that doesn't work, because there's only two phenotypes, magic and not magic.

Can anybody give the quote that says Ted Tonks was a Muggle-born? I was sure he was a Muggle, but I haven't my book with me to check...

OotP, chapter 3. p 50 (American hardback):

"Very clean, aren't they, these Muggles?" said the witch called Tonks, who was looking around the kitchen with great interest. "My dad's Muggle-born and he's a right old slob. I suppose it varies, just like with wizards?"

and chapter 6, p. 113:

"Andromeda's sisters are still here because they made lovely, respectable pure-blood marriages, but Andromeda married a Muggle-born, Ted Tonks, so--"

That was very interesting. While it may not seem valuable I think it is cool to look at the books from a scientific point of view (but I am really into biology). And it is at least as valuable as just predicting the plot of the next book.

Multiple alleles, not multiple genes, control blood type - that I remember off the top of my head. You're right, though, that there are only two phenotypes.

I've another idea - though it is of course impossible to prove in any way.

What if genes determine whether someone *could* be magical - that is to say, whether magic could enter into them - but the actual presence of magic is, well, magical?

Wow. Congrats on mastering Mendelian genetics. You will find as you advance in your genetics studies, however, that many highly variable traits (something that falls in a wide range) are influenced by 9 or more genes. Skin color, height and intelligence are all coded by many more than 2 genes. Surely magic (hypothetically) would be considered highly variable (powerful v. weak wizards) and its inheritance would therefore be much more complicated than THERE or NOT THERE. Just a thought!

I don't have time to read everyone's responses because I'm on a limited lunch break so if someone already mentioned this, my apologies for the redundance.

This very logical genetics explanation made one particular point which stuck with me

"is it possible that there are anomalous abilities which are more common among those who have some Muggle ancestry?"

It makes me think of inbreeding. Sometimes the better, stronger, faster breeds are those of mixed parentage. In dogs, mutts tend to have a sweet disposition and a long lifetime whereas a lot of purebred dogs (I'm not saying all purebreds but a lot) have a more unpredictable disposition. I also noticed purebred dogs also tend to have a tendancy towards health issues. Maybe its the mixing of bloods and races that is making the muggleborn and halfblood wizards and witches excel in certain things. I'm not saying that pureblood wizards don't excel but don't Crabbe and Goyle seem like your stereotypical inbred folks? Malfoy is very intelligent but has an unpredictable personality.

With regard to whether Tonk's father is a Muggle or Wizard, as far as I remember, Muggles were called Muggles whereas a witch or wizard of Muggle parentage was called Muggle-born. From symantecs one could argue that Tonks was a wizard. I could swear that it was said somewhere else that her dad was a muggle but to be burned off of the Black Family Tree, one only had to consort with a non pure-blood.

I really enjoyed this editorial. I've been wondering about how magic works genetically for a long time and this is the most convincing explanation I've heard. Great job!

So, generally half-bloods are more powerful than the rest?

Where do the Weasleys, the Malfoys and the Blacks fit in? Are they less powerful or are they just exceptions? If you ask me, memebers of these families are generally more powerful than the rest and they are pureblood.

Thank you for this editorial. As a high school Bio/Chem student and a prospective Biology major in college, it's always cool to see two of my favorite things (Harry Potter and genetics...I'm such a nerd...) combined.

Since you wrote this editorial (as opposed to earlier ones, which suppose that the genes are Mendelian), surely you know that genetics are often far, far more complex than Mendel said they are, especially in complex organisms for humans. Eye color alone is controlled by three seperate genes, and hair color has at least two genes. I always figured the gene for Magicness (if there is one) would be incredibly complex.

You already said exactly what I wanted to post. I am a microbiology major and I just finished a class in Modern Genetics this semester. I also assume the genetics of magic to be much more complex than even this article mentions. Although you did a good job of explaining why squibs and muggleborns can result due to genetics.

Nice...

Except for I have read somthing pretty much the same as this in a science magizene I read at school.

Nice...

Except for I have read somthing pretty much the same as this in a science magizene I read at school.

The only magazine I consulted on this was Orchids, The Magazine of the American Orchid Society. I did a little internet research to confirm what I remembered of the long-ago article, and to give credit to the person who discovered that there were two types of white Cattleyas. It wouldn't surprise me if several people had reached the same conclusions independently. I'd be interested to see how someone else presented the theory, however. Would you send the name and date of the magazine and the title of the article? TIA.

Thank god I studied genetics in science or I would have no idea what this person was talking about. A theory I have about this is that Hermione's mother may be a carrier for magic (since only females can be carriers). But if magic is really a dominant allele (type of gene) then that can't be true or Mrs. Granger would be a witch. Perhaps Hermione's mom is a squib? Or it could be her dad that's a squib. Even if one of her parents was a squib why did they not tell her when she got her letter? Who knows, I could be totally wrong about all of this.

Thank god I studied genetics in science or I would have no idea what this person was talking about. A theory I have about this is that Hermione's mother may be a carrier for magic (since only females can be carriers). But if magic is really a dominant allele (type of gene) then that can't be true or Mrs. Granger would be a witch. Perhaps Hermione's mom is a squib? Or it could be her dad that's a squib. Even if one of her parents was a squib why did they not tell her when she got her letter? Who knows, I could be totally wrong about all of this.

I wasn't suggesting that either magical gene was on the X chromosome - as far as I know, that's the only kind of gene for which only females can be carriers. (Things like hemophilia and male pattern baldness are sex-linked traits - since females have two X chromosomes, they can "carry" the alleles for either of these traits without having the conditions, as long as they have a dominant allele on the other chromosome. Since males only have one X chromosome, if they get the "wrong" allele from their mothers, they're stuck - there's no dominant allele to override it.)

Hi T Brightwater! Excellent editorial. The phenomena you are discussing is called "epistasis" (which means: to stand upon), because the dominant phenotype is seen in an A_ individual only if the B_ genotype is also present. This is seen in a lot of other systems besides the orchids, though they are an excellent example. There are traits that are dependent on three loci where the dominant phenotype is seen only in A_ B_ C_ individuals. The Punnet squares get to be a real mess.

It makes sense that "magic" in the HP universe is a dominant trait because it is a positive function that some people have but others don't. Most dominant traits involve the ability to produce an enzyme that is lacking in individuals with the recessive phenotype. For example: the ability to taste phenylthiourea is dominant. Those of us with the aa genotype lack the ability to make a particular taste receptor and cannot detect the presence of this nasty tasting compound. Another example of an interesting dominant phenotype is bithorax in fruit flies. Flies with one copy of this dominant allele have four wings. This is an example of a gene that regulates a whole set of other genes and thus controls the development of a body segment.

"Magic" may be rare in the human population of the HP universe because it is not a beneficial trait. (Wizards can live a longer than average life. But it seems like an awful lot of them don't live longer than Muggles because they get murdered.) An example of a dominant but rare trait in the real world is achondroplasia. One copy of this allele causes a person to be a dwarf, with short arms and legs. Two copies of the achondroplasia allele is a fatal condition. This is a gene that suppresses bone development. (Again, it's a gene that regulates other genes.)

Another interesting complication is the issuee of penetrance. There are some dominant alleles that are expressed in Aa individuals, but they aren't always expressed. Some Aa individuals show the dominant trait and others don't. This may be due to epistasis but it can also be due to non-genetic factors such as diet.

Thanks for all the information, king!

"Magic" may be rare in the human population of the HP universe because it is not a beneficial trait. (Wizards can live a longer than average
life. But it seems like an awful lot of them don't live longer than Muggles because they get murdered.) An example of a dominant but rare trait in the real world is achondroplasia. One copy of this allele causes a person to be a dwarf, with short arms and legs. Two copies of the achondroplasia allele is a fatal condition. This is a gene that suppresses bone development. (Again, it's a gene that regulates other genes.)

As Professor Koniphorus Swamp points out in his/her essay (HP Lexicon), pure-blood wizards (except for the Weasleys) also seem to have a bad record in passing their genes on, which may also contribute to their scarcity.

I wonder if Parseltongue might be a condition comparable to achondroplasia - a rare dominant trait. Perhaps having two copies of the allele leads to misaligned eyes or one of the other "inbred" characteristics of the Gaunts.

So I am a little behind in my editorial reading but for other like minded scientists and biologists who are avoiding work something a bit less trival... I propose another hypothesis.
Any one who has studied college leval genetics will understand this.. but for the rest I will try to clarify. What if it was not one gene, or two genes but a few pieces of a more complex network. Current genetic theory goes far beyond Mendel's punnet squares and looks about how different genes regulate each other by turning each other on and off based on many different types of imputs, as well as the classics of genetics looking at mutations from a parent. What is interesting about this is that just because an individual does not have a working copy of that gene does not mean that they will have a defect. There may be several genes which serve simular purposes and can take the place of each other. While this sort of analyis cannot be used to generate a % of individuals that will display the trait it could be interesting in looking at how some traits appear so differently in different wizards.
We know that some wizards have extrodiary talent and others have barley any at all.

I don't necessarily think magicness has to be as complicated as what is proposed here - 2 genes and at least one dominant allele from both genes to produce a wizard.
This assumes that the traits are non-continuous. That is, a person is either magical (A-B-) or not (A-bb, aaB- or aabb). But - the different combinations of alleles of the two genes can't contribute to varying degrees of magicness.
This model says that anyone with the A-B- alleles shows the same amount of magical ability - whether AaBb or AABB.
You may think that perhaps the number of dominant alleles contributes to the amount of magicness. Yet this would mean that Hermione (more likely AaBb) should show less magical ability than someone like Neville, a pureblood and likely to be AABB - when we know she doesn't!
When a muggleborn like Hermione can show just as much, if not more, magicness than purebloods and Neville's magicness is closer to that of a squib's - clearly we're missing something!

It really could be as simple as one gene involved in magicness!
If you assume that the wizarding gene is recessive, this accounts for the muggleborns. (And explains why there seem to be more muggles than magic-folk).
Mm and MM = muggle.
mm = wizard.
To account for squibs (bearing in mind that they are rare compared to muggleborns) and varying degrees of magical ability there is expressivity and penetrance.
Expressivity (the degree of expression of a genotype into phenotype) explains how the wizarding alleles can be expressed more in some people (like Hermione) and less in others (like Neville), regardless of their ancestry.
Penetrance (the percentage of a population with the same genotype expressing the same phenotype) means that even though a person has the alleles 'mm' they may not express the magical phenotype and is therefore a squib.

...I've probably looked into this too much... maybe it does all just happens by magic!
Email me if you have any comments/complaints/discussions:
torre_degli_angeli@hotmail.com


p.s. Even though this doesn't seem relevant to the whole HP plot...
bear in mind that Voldemort is a very powerful wizard and a half-blood, and he fears Dumbledore - a more powerful wizard and who, we assume, is a pure-blood...
If magic is genetic (and there is something about their genes that is expressing an enormous amount of magic) clearly the origin of the wizarding allele matters not - whether from a muggle or a pure-blood parent, the degree of magical expression depends on the person. Thus Voldemort's war against muggles and muggleborns (and anyone who stands in his way really..) is in vain if the magic has nothing to do with where it is derived. It just reminds us all the more to look at each person separately and not judge them by their families..

I'm rambling now... goodbye.

Lupin is a half-blood, according to (I believe), the World Book Day chat. It just annoys me when he is always left out of the list of half-bloods (the Lexicon does this too). Of course, we don't know if his "non-pure" parent was a muggle or a muggle-born.