[HPforGrownups] Wizarding Genetics

[Robert Shaw]

No: HPFGUIDX 85094

MadameSSnape at aol.com wrote:

> Taryn wrote
> Y'know, that brings up an interesting question of how exactly
> wizarding skill is transmitted from person to person. JKR seems to
> imply here that it's genetics, using the example of two parents with
> dominant genes passing recessive genes to a child--hence, two
> black-haired people producing a redhead and "no one knowing why."


> Sherrie wrote:
>
> Hmmm.... :::playing with Punnet's squares:::  My theory is that the
> Wizarding gene is a dominant mutation - that is, the allele isn't
> present in the "normal" genetic makeup of the parent generation, but
> somewhere along the line something changes on the X chromosome (has
> to be X-linked - otherwise, there'd be no Hermione) that enables the
> magical ability.


Punnet squares are an idealisation. Genetics is often a lot more complex
than that.

I can think of three other options, all with real world precedent.

First option. The magic gene could be a segregation distorter.
There are many genes known which cheat. They actively interfere with
various stages of reproduction to make themselves more likely to be
inherited.

E.g suppose muggle fetuses are killed by their intimate exposure to
magic when their witch mother cast a spell, or use a potion, during
pregnancy. (Alternatively eggs/sperm that don't carry the magic gene
get killed whenever a spell is cast. There are several other variants on
this theme.)

Then witches would only be able to have magical children, apart from
a few rare cases where a mutation protect the muggle from magical
side effects (i.e squibs.)

In this case we'd expect a low fertility rate in  wizard-muggle
marriages.

Second option. There are environmental factors.

The ability to learn to read is genetic. Virtually all humans have the
right genes for it, no chimps do. However not everyone who can
learn to read does.

Similarly the magic gene might give the potential to learn magic *if the
environment is right.*

The Hogwarts quill shows that the environment has no influence after
birth (either that or its very good at divination) but there are nine
months
before birth.

Suppose that having two copies of the magic isn't enough to be a wizard,
you must also be exposed to a sufficient level of magic while still in
the
womb, when the brain is being formed.

In effect, the magic gene would need a jump start from outside.

Then the magic gene can be very common, conceivably to the point where
over 90% of muggles have one copy and 80% have two, and yet we can
still have only one muggle-born in 10,000 or less.

Wizards don't normally cast spells on pregnant muggles, and they keep
all muggles away from magic so most of the people with two magic genes
wouldn't get the necessary pre-natal exposure to magic, and their magic
genes would never switch on.

In this case virtually all children of wizard-witch marriages would have
magic, apart from a few mutations/squibs.

Wizard-muggle marriages could have 80-90% wizard children
(same as the frequency of the gene in the general population) since
whether
the mother was witch or muggle the wizard parent would be using enough
magic near the fetus to trigger the magic gene.

Some of you should now be asking how the whole thing started.
The first wizard can't have had their magic triggered by the spells of
their parent.

Well, humans aren't the only users of magic, and the genetics may
be different in different species. A close encounter with a unicorn
or dragon while pregnant could be enough to kick start the child's
magic.

Third option. There might be hundreds of genes involved.

Suppose there is a set of 30 genes, each of which can say magic
or muggle; some recessive, some dominant. You only get to be a
wizard if at least 20 say magic.

Wizard-witch marriages will produce magical children, unless they
are unlucky with the draw.

In wizard-muggle marriage the wizard parent will contribute over
two-thirds magical genes. Provided the frequency of these genes
in the muggle population is reasonably high, the muggle parent will
throw enough in to produce mostly magical children.

In a muggle-muggle marriage the odds are strongly against enough
recessive magic genes matching up, even if they are quite frequent.

This option too would produce the observed pattern.

These three options aren't mutually exclusive either. Maybe magic
needs both the right prenatal environment and the cooperation of
a few dozen genes.

--
Robert