Harry Potter and the genetics of inheritance

"Who we are is the genes we’re born with and the experiences we have."

Harry Potter's Hogwarts School of Witchcraft and Wizardry

With the global popularity of Harry Potter, kids (and adults) all over the world secretly hope for their acceptance letter to Hogwarts School of Witchcraft and Wizardry.

While the books and movies can whisk you off to Harry’s magical land of fantasy, real-world science can help explain if you would or could have magical powers, using the basics of genetic inheritance and the beloved characters we meet as examples.

“It’s a fun topic, mixing real genetics into the world of Harry Potter,” says Robert Pyatt, Ph.D., director of the Sanford Medical Genetics Laboratory and fellow Potter-head. “What we’re talking about is the connection between genetics and whatever feature they’re connected with,” whether that’s a physical trait or the ability to do magic.

Wands at the ready, readers: Dr. Pyatt is about to walk you through some examples of real genetic principles in the world of Harry Potter.

How traits are passed down

Red hair and freckles seem about as common in Harry Potter’s world as it is in ours. But for Arthur and Molly Weasley’s family, it’s not just common — it’s a given.

“With genetics, we often look at the inheritance pattern,” Dr. Pyatt says. “Or if you look at a family tree, what’s the pattern of a feature or a trait that’s being passed down from generation to generation, from parents to children.”

Traits are passed down through what’s called dominant or recessive genes. “With dominant genes, you typically only inherit one variant or one change in the gene that’s connected with a specific trait or feature, and that’s enough to let you express that trait or feature — a great example of a dominant trait is freckles,” Dr. Pyatt explains. “It’s changes in the melanocortin 1 receptor (MC1R) gene that will show in a person as freckles.”

The same gene that’s associated with freckles is involved with red-colored hair. But instead of being dominant, changes in the MC1R gene that cause red hair are recessive, meaning two changes in the gene need to be inherited for the trait to be displayed in the person.

Since both Arthur and Molly Weasley have red hair, they each have two copies of that change in the MC1R gene, and they’re both going to pass that on to their children.

“So because they both share the same genetic changes in that MC1R gene, 100 percent of their children are going to have red hair,” Dr. Pyatt says.

“We all have interesting genetic changes,” he says, but it’s just a little more obvious with some, like the Weasleys, because of a particular trait.

Inherited magical abilities

This same idea of dominant and recessive genes can be used when looking at how Harry Potter characters inherit the ability to use magic.

“If you look at Harry’s pedigree or family tree, both his parents can use magic, and he can use magic,” Dr. Pyatt says. “His father’s family can use magic, but his mother’s family can’t. If you look at that, it suggests a recessive pattern of inheritance, where Harry is inheriting one variant from his dad, and one variant from his mom. So he has two changes in whatever gene is connected to using magic, and that’s allowing him to use magic.”

But what about Hermione, who was born to two Muggles, or people who don’t have magical abilities?

“Neither one of her parents can use magic, so in this case, because it’s a recessive condition or recessive trait, we think of Hermione’s parents as being carriers,” Dr. Pyatt says. “They likely have one change in that gene for the ability to use magic, but they only have one — so they carry that trait, but they can’t actually express it. They can’t use magic themselves. But if they each pass down that trait to Hermione, she inherits both changes in that recessive gene, and she can use magic.”

Magical variations

There’s also some characters who have magical parents, but no magical abilities themselves — Squibs, as they’re called, like Filch and Mrs. Figg.

“To possibly explain that, there’s two principles that we normally see with dominant traits, but with this discussion, we’re going to add them in for recessive traits,” Dr. Pyatt says.


“So one of those principles is something called penetrance. In a lot of cases when you have a change that’s associated with a trait, 100 percent of the time, you express that trait. That’s called complete penetrance,” he says.

For example, variants or changes in the CASZ1 gene are associated with heart defects. “Everyone who has one of these variants is born with a hole in the wall between the lower chambers of their heart,” Dr. Pyatt says. “In this case, changes in the CASZ1 gene shows complete penetrance for ventral septal defects.”

There’s also incomplete or reduced penetrance, where you may inherit the genetic change or variant, but you may not always express that trait or feature.

“The trait may be seen in 80 percent of people with the genetic variants, or 20 percent — any percentage is possible. But it’s less than 100 percent,” Dr. Pyatt says.

For example, in one study, 72 percent of women with variants in the BRCA1 gene and 69 percent of women with variants in the BRCA2 gene developed breast cancer by age 80. There’s an incomplete penetrance of whether the change in the gene will result in cancer.

“It’s like a light switch: It’s either on, and the trait is expressed, or it’s off, and the trait isn’t expressed,” Dr. Pyatt says.

“So if we had incomplete penetrance going on in Harry Potter, it may be that somebody like Filch actually inherited the genetics to use magic, but because there’s incomplete penetrance, he actually can’t show that trait of being able to use magic.”


The second principle is called variable expressivity. “This relates to when you have the trait, but how distinctive that trait is can vary from person to person,” he says.

“Polydactyly, or the presence of extra toes, is a great example of a trait that shows variable expressivity in cats,” Dr. Pyatt explains. Polydactyly is inherited in a dominant pattern, but the expression of that trait can vary, as the number of extra toes can differ greatly from cat to cat.

“So it may be that somebody like Filch or Mrs. Figg inherited those traits to be able to use magic, but they may have such variable expressivity, that may be why they can only use it at such a low level they don’t recognize it,” Dr. Pyatt says.

Variable expressivity could also explain why some students at Hogwarts are intuitively much better at using magic than others. “Poor Ron is never that hot at it, but he does the best with what he has, and there are people like Hermione who are just fantastic at it,” Dr. Pyatt says. “Bringing in some of these genetic principles may help explain some of the variation in that feature of being able to use magic.”

It’s not all genetics

Dr. Pyatt cautions not to be too deterministic when it comes to genetics.

“Genetics certainly plays a large part in many of our features and our predisposition to disease. But in nearly every case, it’s not just your genetics, but it’s the environment as well that is playing a significant role,” he says.

What you eat, the air you breathe, the actions you take or don’t take — they can all factor into the changes that occur to your genes throughout your life. But even those are just part of who you are.

“Who we are is both the product of the genes that we’re born with, and the experiences that we have,” Dr. Pyatt says. “The human experience is very much a spectrum. You’ve had great things that happen to you, you’ve had horrible things that have happened to you, and they really shape who you are.”

There are some genetic syndromes where, for example, an individual might be more violent or prone to anger, but there is no one gene for an emotion or behavior pattern. “Even in those genetic conditions, it’s more of a predisposition that you see for those behavior patterns than anything that’s absolute,” Dr. Pyatt says.

The sorting hat at Hogwarts seems to factor in both genetics and behaviors when determining houses that seemingly set students’ loyalties and principles for life — it could sense Neville Longbottom’s Gryffindor bravery before he could, it knew Draco Malfoy’s family lineage and motivations made him a classic Slytherin.

But no genetic or behavioral test in the real world can factor in all the variances and nuances of who a person is to become.

“Thank God for that,” Dr. Pyatt says of those limitations. “I don’t know of anybody that would want that, because you want your children to be able to grow up to whomever they are.”

And that’s the magical part of being human.

More stories with Dr. Pyatt

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