Thursday, August 02, 2007

harry potter and the doubly helix

I'd always presumed muggle-born wizards in the Harry Potter books were the result of a genetic mutation. J.K. Rowling is answering all kinds of questions now about the series, and she says I'm wrong:
Katie Mosher: How exactly do muggleborns receive magical ability?

J.K. Rowling: Muggle-borns will have a witch or wizard somewhere on their family tree, in some cases many, many generations back. The gene re-surfaces in some unexpected places.
This is very perplexing, because magic ability otherwise gives all indications of being an autosomal dominant gene (get the gene from one parent, and you have the trait), but now she's talking about it like it is recessive and so can just lurk around unexpressed in your family tree for generations. Harry had a muggle-born mother, so if the gene was recessive, he'd have had only a 50% chance of being a wizard. Same thing with each Hermione and Ron's two children (assuming Ron is really the real father; if, as is at least as likely, Harry is the real father, then the kids would have only a 25% chance of being a wizard.) There are no indications in the book that when people marry muggle-born wizards they consider there to be a 50% chance they'll have a squib kid.

I feel cheated. I feel like the Harry Potter books are no longer scientifically realistic.

Update:
Ugh, I've only had this post up a few minutes and already a friend has e-mailed to correct me. I feel like a disgrace to Ravenclaw. Obviously, if the gene is recessive, Harry needs two copies, and so he has the same probability of having wizard spawn as any other wizard, and squibhood is the mutation. (Squibs who breed with a slumming wizard would have a 50% chance of having a wizard child.) Rowling's still not right, though. The muggle-born wizard has to have a wizard somewhere on each side of the family tree.

5 comments:

gabriel said...

This letter to Nature makes a similar argument.

jeremy said...

Because of link issues, here is the first letter to Nature:

Harry Potter and the recessive allele

Jeffrey M. Craig1, 3, Renee Dow2 and MaryAnne Aitken2, 3

1. Chromosome Research, Murdoch Childrens Research Institute, Royal Childrens Hospital, Flemington Road, Parkville, Victoria 3052, Australia
2. Genetics Education, Murdoch Childrens Research Institute, Royal Childrens Hospital, Flemington Road, Parkville, Victoria 3052, Australia
3. Department of Paediatrics, University of Melbourne, Royal Childrens Hospital, Flemington Road, Parkville, Victoria 3052, Australia

Sir:

We are bombarded with news of genetic discoveries on an almost daily basis, but people without a formal knowledge of heredity and genetics can have difficulty in deciphering and applying this information. Education and debate across all ages would undoubtedly help, but how can we teach children these concepts?

We believe that successful lessons for younger children can be achieved using analogies of direct interest and relevance. Most children are familiar with J. K. Rowling's stories about the young wizard Harry Potter (whose latest exploit, Harry Potter and the Half-Blood Prince, was published by Bloomsbury in July). They are set in a world like our own, but populated by a minority of people with supernatural powers (wizards and witches) and a majority of people without (muggles).

Wizards or witches can be of any race, and may be the offspring of a wizard and a witch, the offspring of two muggles ('muggle-born'), or of mixed ancestry ('half-blood').

With the use of these examples, the concepts of mendelian genetics can be introduced to children as young as five.

J. M Craig, R. Dow, M. A. Aitken

This suggests that wizarding ability is inherited in a mendelian fashion, with the wizard allele (W) being recessive to the muggle allele (M). According to this hypothesis, all wizards and witches therefore have two copies of the wizard allele (WW). Harry's friends Ron Weasley and Neville Longbottom and his arch-enemy Draco Malfoy are 'pure-blood' wizards: WW with WW ancestors for generations back. Harry's friend Hermione is a powerful muggle-born witch (WW with WM parents). Their classmate Seamus is a half-blood wizard, the son of a witch and a muggle (WW with one WW and one WM parent). Harry (WW with WW parents) is not considered a pure-blood, as his mother was muggle-born.

There may even be examples of incomplete penetrance (Neville has poor wizarding skills) and possible mutations or questionable paternity: Filch, the caretaker, is a 'squib', someone born into a wizarding family but with no wizarding powers of their own.

We believe that, with the use of these examples, the concepts of mendelian genetics can be introduced to children as young as five, and then built on by gradually introducing specific terms such as 'gene' and 'allele', and relating these to chromosomes and DNA. At every stage, the children's familiarity with the Harry Potter characters can be used as a hook to engage them in discussing concepts of heredity and genetics.

jeremy said...

Here is the second:

Harry Potter and the prisoner of presumption

Antony N. Dodd1, Carlos T. Hotta 1 and Michael J. Gardner1

1. Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK

Sir:

Jeffrey Craig and colleagues, in Correspondence ("Harry Potter and the recessive allele" Nature 436, 776; 2005), recommend the use of analogies as tools for introducing young people to scientific concepts. Taking their example from J. K. Rowling's stories about the young wizard Harry Potter, they suggest that wizarding is a monogenic trait, with the wizard allele (W) recessive to the muggle allele (M). We believe the assumption that wizarding has a genetic basis to be deterministic and unsupported by available evidence.

Following Craig and colleagues' analogy, Hermione, as a muggle-born witch, must have WM parents. However, as Rowling fans could point out, Hermione's parents were muggle dentists who lack any family history of wizarding. It's true, of course, that chance may not have thrown up a witch or wizard for many generations, or that any who did have magical powers may have kept them secret to avoid a witch hunt.

What about Neville's apparently poor wizarding skills? These cannot be explained by incomplete penetrance, as Craig and colleagues suggest. In incomplete penetrance, individuals either display the trait or not: they do not display an intermediate degree of the trait. Poor wizarding skills might be indicative of variable expressivity of an allele. However, both variable expressivity and incomplete penetrance are associated with dominant alleles. If the wizarding allele were dominant, rather than recessive as suggested, wizarding children such as Hermione could not be born to non-wizarding parents.

Neville's clumsiness may, perhaps, be an individual characteristic unrelated to his potential powers. However, it is not possible, from the evidence presented so far, to conclude that wizarding is a heritable trait.

anomie said...

Goodness, and I thought my ramblings about the statistical prevalence of evil in Slytherin house was a supreme act of geekdom ;)

Gil said...

Man, can't there ever just be a magic gene? Let's just say that it's not even a gene so much as a grouping of nitrogen bases that has some magic in it. Then perhaps the magic only sometimes reacts and creates the magic proteins to give the abilities, hence the strange popping up. And if they get it from two parents, then it will definitely react from the increased magical powers of two sequences. And sometimes something will block the magic, which causes a squib.

Sometimes it's good to think less like a scholar and more like an idiot.