Harry Potter & Genetics

Hello! Welcome to my first blog post. Today I will be combining two of my favourite things, the Harry Potter books and genetics.

The Harry Potter books were a huge part of my childhood, my whole family loved reading and discussing them. When I was about 10 or 11, I remember desperately trying to work out the mode of inheritance of magic in Harry Potter (I was convinced my dad was a wizard and wanted to know the probability that I was a witch). I didn’t get very far, as my knowledge of genetics only extended as far as very simple punnet squares, but I hope to try and shed more light on the subject now!

First of all, we must compile the knowledge we have about genetic inheritance in the wizarding world. We know that wizards be born from two wizarding parents, two muggle parents, or one wizard/witch and one muggle.

If we treat wizarding as a genetic ‘disorder’, we need to look at a pedigree (or family tree) before we can work out what kind of disease it is i.e. dominant, recessive or co-dominant. In this pedigree, as wizarding is the ‘disorder’, individuals with it will be shown filled in, and individuals without it will be shown clear.

The Black Family

The largest family from Harry Potter with a known family tree, is the Black Family. So we will begin by looking at their pedigree.

Actually, most of this tree doesn’t tell us very much at all about the mode of inheritance, just that wizards seem to have wizarding children and so do mixed and muggle couples, as we can see in the cases of Ted Tonks (I) and Lily Potter (Evans) (II). So, as everyone appears to be having wizarding children, you would assume that the wizarding ‘gene’ is dominant, and this is what is said on the J.K. Rowling official site.

However, if this was true, then no muggle could possibly have the gene for wizarding, and so would not be able to have any children with the wizarding gene. As we can see with the case of Lily Potter, some muggles must be able to carry a wizarding gene, which means it must be recessive to the dominant muggle gene (assuming Mendelian genetics i.e. wizarding or ‘muggle-ness’ is caused by a single gene).

So, we can conclude that the genetic ‘disorder’ of wizardry is autosomal recessive.

Muggle-Borns

As we now know which gene is recessive, we can denote the dominant ‘muggle-ness’ gene as M, and the recessive wizarding gene as m. An individual is only a wizard if they have the genotype mm. Muggles are either homozygous with the genotype MM, or heterozygous carriers, Mm.

In the case of muggle-borns, such as Lily Potter or Hermione Granger, their parents must have both been carriers for wizardry, as one copy of each gene (or one allele) is inherited from the mother, and the other is inherited from the father.

I find it very interesting that muggle-born wizards and witches are, in terms of wizarding ability, genetically equal. I’m not sure if J.K. Rowling did this deliberately, or if she even thought about genetic components while writing the book, but I like the way it ties in with the idea of equality between different backgrounds, as a lot of the story focuses on discrimination about muggle-born and half-blood wizards and witches.

Squibs

Now, where this all begins to fall apart is with individual III, Marius Black. In the books, Marius Black is burned off the Black Family Tree for being a Squib- a muggle born to wizarding parents. For both the parents to be wizards, they must both be homozygous for the recessive wizarding gene, and have genotype mm. If we make a punnet square for two wizarding parents, we can see that, with my genetic model, it isn’t possible for them to have a muggle child.

So we have to look for other explanations for the existence of squibs. One explanation could be that all squibs have some sort of mutation in one of their m alleles, causing it to become the dominant M gene, or just producing a non- or low- functional version of the m gene, causing a lack in magical ability. In human disease, these mutations are usually caused by SNPs (single nucleotide polymorphisms- meaning one base in the code for a gene is changed for another). These are not uncommon in humans, but the probability of multiple wizards exhibiting the same SNP in the same gene is very low, but it is said that squibs are very uncommon, so this could be an answer.

Of course, this is still assuming that muggle-ness and wizardry are just caused by a single gene, and human genetics is rarely that simple. Non-Mendelian genes can be affected by other genetic and environmental factors and are described as multifactorial. If the wizarding gene is multifactorial, it could have varied penetrance within the wizarding population, meaning some individuals could have a wizarding genotype (mm) but not have magical powers.

Wizardry could also exhibit varied expressivity, so different wizards will express different amounts of the m gene. This could account for variations in wizarding ability (some wizards are just better than others in the books) and could also explain where squibs come from, as they could just be wizards with very low expressivity in the m gene.

To find out whether any of these squib theories are correct, we would need to know the proportions of muggles to wizards to squibs in the population, and I really doubt anyone knows the answer to that. So I’m afraid we’ll never know for sure whether my theories are correct.

It is always possible that squibs are just the result of witches having affairs with muggles, and pretending they are their husbands’ children! It could be a massive secret that all witches know about and have covered up for each other for centuries. I quite like that idea, it makes the wizarding world seem much more exciting for some reason!

I hope you’ve enjoyed my first blog post, and I can definitely say I’ve got further with this than I did when I was 10/11.

#text #harrypotter #genetics