The Inheritance of Magic: What it Means to the Wizarding World
An original editorial by Beansprout Wilkins
This particular editorial has been brewing in my mind since JK Rowling first added a section on Squibs to the Extra Stuff section of her official website many months ago. It was one line in particular that has led me to formulate my thoughts on the subject of wizarding genetics into a semi-coherent, organized editorial: "Squibs are rare; magic is a dominant and resilient gene." Due to the importance of heritage in the Harry Potter
series (and my own status as an extreme science nerd) I had actually contemplated the inheritance of the magic gene before Jo had issued a statement on the subject. Jo's assertion that "magic is a dominant and resilient gene" turned the theory I had formulated completely upside down. A basic understanding of Mendelian genetics is required in order to follow this editorial, so it seems a brief science lesson is in order. For those of you scared off at this point, rest assured, I really do mean basic
; no remarkable scientific aptitude is required. In fact, those of you with even a vague recollection of high school biology can scroll past the next section.
A Quick Genetics Lesson
When we are attempting to evaluate a trait as strictly dominant or recessive, we are making the assumption that this trait is controlled by only one gene. Each individual gene is made up of two alleles, or gene variants. In traits that are strictly dominant or recessive, there will be only two variants. An uppercase letter represents the dominant allele, while the recessive is expressed by a lowercase letter. For any given trait, a child receives one allele from each parent. If a person has two of the same allele, they are homozygous for that trait. If one of each variant is present, that person is described as heterozygous for that trait. The trait expressed is known as a phenotype, while a description of all alleles present is known as a genotype. Let's do an example using the curly hair gene, which is dominant over straight hair. Let C represent the curly hair allele and c the straight hair allele. If parent A's phenotype is curly hair, but that parent is heterozygous for the trait, the genotype would be Cc. If parent B's phenotype is straight hair, the genotype is cc. If a person expresses the recessive trait, they must be homozygous for that allele. If parent A and parent B reproduce, parent A has a 50% chance of passing on the curly hair allele, and a 50% chance of passing on the straight hair allele. Parent B can only pass on the straight hair allele. This means that these parents would have a 50/50 chance of having curly haired children, but all of them would be carriers of the straight hair gene. Now that we have the necessary understanding of these genetic principles, we can apply them to magic inheritance.
Magic as a Recessive Trait
Before Jo released her statement that magic is a dominant gene, I had come to the conclusion that magic's gene was, in fact, a recessive one. Suppose that M represents the non-magic gene, and m the magic gene. This means that all wizards and witches have the genotype mm. This also means that there could be Muggles out in the world with a heterozygous genotype of Mm, meaning that they are carrying the magic gene. Should two Mm Muggles have children, their offspring would have a 25% chance of being magical. This number seems to fit with the prevalence of Muggle-borns at Hogwarts. This would also make Squibs impossible unless a genetic mutation took place, meaning squibs would be quite rare, which, according to Jo, they are. Also, genetic mutation is more common when inbreeding occurs, which is frequent in the pureblooded families of the Harry Potter world, and a Squib is specifically a non-magic child in an all-magical family, thus making mutations a very real possibility.
The one hole in this logic is the idea of half-bloods. If a wizard (mm) marries a Muggle, there are two possibilities: that the muggle is a carrier of the magic gene (Mm) and thus their children have a 50% chance of being magical, or the Muggle is not a carrier (MM) and thus their children have no chance of being magical. This makes half-bloods seem a fairly unlikely possibility, yet the in the Harry Potter universe, half-bloods seem to out number all others, to the extent that it would seem that a marriage between a wizard and a Muggle almost always results in magical children. But, if magic were a recessive gene, then this would not be true. Even if we are to assume that all Muggles carry the magic gene, the child of a wizard and a carrier of the gene still only has a 50% chance of being magical. Statistically, it seems that more than half of these children show magical ability, which is inconsistent with the inheritance rates, not to mention the unlikelihood that most Muggles carry the magic gene.
Magic as a Dominant Trait
The next possibility is that magic is, as Jo says, a dominant gene. In this case we would assume that truly pureblooded wizards would be homozygous for the magic allele, meaning they would have a genotype of MM (we will now reverse the letters as assigned in the previous section, using M to represent magic and m for non-magic). In this case, a pureblood who has children with a Muggle or Muggle-born wizard would produce magical offspring one hundred percent of the time, but their children would be carriers of the Muggle gene, ultimately increasing the chance of non-magical births in later generations. If we are to believe what Hagrid tells us in PS/SS, that there are really very few or no truly pureblooded wizards left, we can assume most wizards have a genotype of Mm. In this case, a marriage between a wizard (Mm) and a Muggle (mm) would produce non-magic children 50% of the time, which is just too frequent to be conceivable, and a marriage between two wizards, both Mm, would produce a Squib 25% of the time. Here is the problem with magic being a dominant gene: it would create an incredibly high incidence of Squibs, a phenomenon that Jo describes as rare. One quarter of births is not rare. The biggest problem with magic being a dominant gene is that it makes Muggle-borns nonexistent except in the event of a genetic mutation. Given the large number of Muggle-borns at Hogwarts and in the rest of the wizarding world, it is impossible to chalk it up to genetic mutation.
Most traits are not determined by only one gene with two possible alleles. There are examples of co-dominance (such as blood type); however, this does not make sense in our context as we are dealing with only two outcomes, non-magic or magic; co-dominance creates multiple possibilities (i.e. blood types AB, A, B, and O). The final possibility is that several different genes control magic. For example, at least three separate genes control human eye color. It is impossible to speculate how multiple genes could be working to create magic in witches and wizards with the information we have from the Harry Potter books, but what we do know is that multiple genes could work in some way to allow for the high percentages of half-bloods. Despite the improved explanation for half-bloods provided here, it makes the idea that magical families will have magical children, and the whole concept of magic inheritance, far less cut and dry than it seems to be in the Potterverse. The main problem I have with the multiple gene theory is that it seems to lead to a correlation between bloodlines and magical ability since it arises issues of partial dominance. For example, of three known eye color genes, two of them contain either brown or blue alleles, and the last contains blue or green alleles. Blue is recessive to green, which is recessive to brown. Thus green eyes occur when both blue/brown genes have only blue alleles, but the blue/green gene has at least one green allele. If any gene has a brown allele, the result is brown eyes. Blue eyes will appear only when all alleles are blue. We also know that there is more at play than science can explain thus far as these colors come in wide ranges, and can also be joined by gray or hazel. These varying levels of dominance and multiple genes at play involved in magic would actually mean that magical ability is dependent on genetics. Any such linkage is explicitly denied in Harry Potter as we see all levels of power dispersed equally among Muggle-borns, half-bloods, and purebloods.
Implications in the Wizarding World
While this editorial may seem like the trivial ramblings of a science nerd (ramblings of a science nerd? Certainly. Trivial? Nope.), whether magic is a dominant or recessive gene has serious implications in the wizarding world. If magic is a recessive gene, all magical people have the same genotype: mm. In effect, Muggle-borns are genetically identical to purebloods. This fits perfectly with the mentality of Dumbledore's point of view that all witches and wizards are equal and should share their world. This also keeps with the portrayal of Voldemort and his followers as maniacal pureblood elitists whose views have no real reasoning and are simply bigoted. Now comes the biggest reason that I truly believe magic cannot be a dominant gene, and consequently the number one reason I continue to believe that magic must be a recessive gene: if magic is a dominant gene, marrying pureblooded wizards (MM) to Muggles, Muggle-borns, or half-bloods (Mm or mm), is actually hazardous to the magic gene. As generations continue to mix heritage, the incidences of non-magical children being born to wizarding families will continue to increase until there is an actual extinction of magical persons. This would give Voldemort's cause (not the murderous aspects, just the anti-Muggle-born ideas) a legitimate argument: that they are literally fighting to protect the survival of magic in humans. If this were true, we would see far more supporters of Voldemort, and far fewer on the light side. It is only natural for any group of people to seek protection of their race and continuance of that race in the future. The dark side is no longer made up of psychotic bigots, but of those seeking to preserve their world and fellow citizens of that world. The way so many in the wizarding world see Voldemort and the Death Eaters as unfounded to the point of ludicrous suggests that there cannot be any justifiable basis for their system of beliefs.
It is clear that magic cannot be a dominant gene. For the same reasons, magic is likely not made up of multiple genes, as this would create partial dominances that would lead to a validation for the discrimination between those of varying amounts of wizarding blood. By process of elimination, we can conclude that magic is most likely a recessive trait. The only initial problem with this explanation is that it seems the probability of marriages between a Muggle and a witch or wizard producing magical children is relatively low; however, we do not actually have any way to gauge how often such unions result in magical children as opposed to non-magical children, since our point of view is Harry's and is firmly cemented in the wizarding world, which is not a place where we would expect to see non-magical children. It would seem to us that magical children are more common in these marriages simply because that is the outcome that we can see in the wizarding world, while the opposite result is obscured from our observations. This possibility makes the idea of magic as a recessive gene even more plausible. The most important aspect of understanding magic to be a recessive trait is that it does truly mean Voldemort and his supporters are nothing more than pureblood supremacists with baseless beliefs. Ironically, perhaps a lesson in Muggle genetics would help them to understand that Muggle-borns are not a threat to their way of life. Based on the evidence I think we can safely say that the way Jo has written the magical world she has, in fact, created magic to be a resilient trait, but certainly not a dominant one.
Please keep in mind that this editorial was written by an eighteen-year-old student who is by no stretch of the imagination a genetics expert.
Posted by: Katie