Wizards, Muggles, and Genetics (long and obsessive)

[dungrollin]

No: HPFGUIDX 119754


Dungrollin wrote:
> So if the magic  gene is dominant, then for Lily to have been a 
> witch, at least one of her  parents must have had at least one 
> copy of the magic gene.  That  would make one of her parents 
> magic/muggle or magic/magic â€" ie, a witch or  a wizard. 
Geddit?)
> 
> 
Amber replied: 
> Not necessarily.  You're forgetting how genetic variation  
> happens.  Genes can mutate into original forms (there was no one 
> afflicted  with hemophilia in the royal families of Europe before 
> Queen Victoria's  children) <snip>

Muggleborns are not mutants, as a quick calculation will show:

The human genome is 3 billion base pairs long. (Base pairs are the 
things that are linked together to make DNA, and are what change in 
a mutation).  Lets be wildly optimistic and say that it takes only 
one base pair change (mutation) to turn a muggle into a wizard, okay?

Birth rate in 1980 was 13.5 per 1,000 population.  The population in 
the UK was around 55 million, and there is on average 1 base pair 
mutation per generation – i.e. there is one base pair difference 
between you and your parents *which is due to mutation*.  

Right.  Some quick maths...

(55,000,000 / 1,000) x 13.5 = 742,500 children born in the UK in 
1980, each of which had a 1 in 3 billion chance of having the right 
mutation to make them a wizard.

Therefore the number of wizards born to muggle parents in 1980 
should have been around 
742,000 / 3,000,000,000 = 0.00025.

Therefore, I can confidently say, that if muggleborns are the result 
of mutations, you would get (in the UK if the population stayed 
static) on average, one muggleborn wizard every 4,000 years.

Convinced?*


Amber continued:
... and some genes can negate the indications of other genes (some  
children are born with the predisposition to cystic fibrosis and do 
not develop  the disease due to other gene combinations--evolution 
at work).  All this  only reinforces how rare muggle-born (25% or 
less of the wizarding  population)  and squibs are.


Dungrollin again:
That's more possible...  Postulate one gene for muggleness/wizardry 
and another gene for a suppressor/expressor.  The active suppressor 
allele would have to be recessive (to allow JKRs statement 
that 'magic is dominant') - but if you've got a large enough Muggle 
population (which we have) with, say, a very low frequency of the 
dominant allele which allows the magic gene to be expressed then... 
Well, you could have loads of wizarding genes in the Muggle 
population, but it's only when they happen to be born into a body 
carrying the dominant expressor gene that the child ends up being
magical. 

Oh god.  Gene frequencies means we're straying into the realms of 
population genetics, which frankly makes me want to go to the pub 
and pretend I didn't suggest it.  

But since JKR has brought genetics into it all, shouldn't we all be 
wizards by now?  Magical genes seem to me to possess huge selective 
advantages over Muggle genes, they should have out-bred us yonks ago.

Dungrollin
Thanking Charme very much for bringing up a subject that I can 
obsess over, but gracefully bowing out now...

* Have I got that right?  Or is it one mutation per generation in 
introns (coding DNA)? - If I'm wrong then the chance is not 1 in 3 
billion, but 1 in 72 million which means... 
742,000 / 72,000,000 = 0.01 (1 muggleborn every 100 years - still 
too low, anyway).