Genetics (longish)

[tigerpatronus]

No: HPFGUIDX 88919

--- In HPforGrownups at yahoogroups.com, "drjuliehoward" 
<drjuliehoward at y...> wrote:
> I have a strange question that I know has been touched upon in some 
> ways by past posts.  It has been 17 years since I had genetics so 
my knowledge is very rusty.  How is magic passed down genetically?  
> 1.  It cannot be Dominant, given that there are squibs and 
mudbloods.
> 2.  It cannot be complete recessive, given that there are 
halfbloods.
> 3.  At what point is a wizard a pureblood?  
> 4.  Is magic genetic at all?

Tigerpatronus here: 

Well, I'm not a geneticist per se, but my PhD is in molecular 
virology and my postdoc is in neuroscience, so I have some knowledge 
of genetics. 

If there is genetic componant to wizardry, the genes obviously have 
low penetrence, which means that the genes may influence your chances 
of having magic, but other factors (environmental, intangible) also 
contribute. 

A good example would be late-onset Alzheimer's Disease (near and dear 
to my heart right now, and thus my model for everything.) There are 
three alleles (form of a gene, like blue or brown eyes) that you can 
have for the ApoE gene. The most common allele for the ApoE gene in 
the US and globally is ApoE3. The "3" is the important part. A less 
common but seemingly protective allele is ApoE2. Remember that you 
have 2 alleles for each gene, one from your mom and one from your 
dad. If you have any combination of "2" and "3" alleles, (2/2, 2/3, 
or 3/3), your changes of developing AD by age 90 are about 20%. But 
one in five people gets it. No one knows why. 

(Note that the above notations are not fractions but representations 
of two alleles. Thus "2/3" does not mean "two-thirds," but "an 
ApoE*2* allele and an ApoE*3* allele.) 

The ApoE4 gene is the "bad" one. If you have one "4" allele (genotype 
of either 2/4 or 3/4), you have about a 50% chance of getting AD by 
the time you're 90. But half of people will be just fine. 

If you have two "4" alleles, (4/4), you unlucky person, you have a 
91% chance of getting AD by the time you're 90, but 1 out of ten 
people with this genotype are walking around, just fine. Call them AD 
Squibs. 

So here's the summary: no genotype is absolutely protective against 
AD. No genotype is absolutely predictive of AD. Other factors 
prevail. It must be so with magic. For a quick summary of other AD 
factors, see the bottom of this post. 

That said, I deeply hope the answer to your question is your #4 (no 
genetic component). 

OT: When, in the new Star Wars trilogy, they 
introduced "midichlorians," (obviously a corruption of the term and 
concept of mitochondria,) I was incensed, and I can't take the SW 
franchise even the slightest bit seriously. Indeed, my acquiescence 
to seeing the second installment involved several blenders-ful of 
strawberry daqueris. 

Back to HP: One of the lovely aspects of the HP saga is that the 
story is about philosophy and characterization and humanity, which 
are the rhelm of fiction, and not about the science of wizardry. 
(Why? Because it's *magic,* that's why!) I think mixing science or 
sci fi (genetics) with fantasy diminishs both. 

I don't want to offend anyone with this next part. If your religion 
is literalist and is very important to you, please stop reading here. 
You have a perfect right to your beliefs. But stop reading here. 

Mixing scifi into fantasy is akin to creation science. It's neither 
fish nor good fowl (slight pun intended.) Creation science and other 
scientific methods that attempt to prove the existence of G-d or 
other deities are misguided and are not good religion and are 
certainly terrible science. 

Anyway, my $.02. 

TigerPatronus


Other factors that are protective against AD (or, how to keep reading 
the HP saga well into your 90s): 
     Eat a fish per week. (50% reduction in AD incidence.)
     Take Advil. (More than 2 years constant dosage with ibuprofin 
reduced AD incidence by 50%. No other NSAID or pain killer was 
effective. NSAIDs have GI complications. Consult an MD.) 
     Learn. Study. Read. (Higher education appears protective, 
perhaps by 30%.) 
     Anti-oxidant therapy. (At least delayed progression.) 
     Treat thyroid disease. (Thyroid disease may be involved in 
neurodegeneration.)
     Smoke. Then stop. (I hesitate to mention this one, as no one 
wants to be accused of promoting a habit that causes heart disease 
and lung cancer, but there is a correlation. It is unknown if there 
is a selective mechanism involved, such as the possibility that 
smokers don't live long enough to develop AD because they all die of 
smoking-related causes, or maybe that smokers who survive smoking are 
nearly immortal and not even AD is going to kill them, or if there is 
something neuroprotective in the tobacco. Receptors that attach to 
nicotine have been mentioned as possibly interacting with some of the 
players in AD, such as the beta-amyloid protein.) 

TK