Hi Hal...
what you do is sort of run it like a typical Mendelian square....
So with a normal person aa (one a on each chromosome)
A person with one extra repeat is aaa (one a on one chromosome and a
duplication of the repeat area on the other chromosome)
Normal person X Normal person
aaXaa = aa or aa normal people
then at a vanishingly small frequency (choose a percentage of your population)
you get one person from normal parents that is
aaa just due to mutation or what ever other epigenetic effect you want.
Normal person X one extra
aaXaaa
Normal a | a
Odd aa aaa aaa
a aa aa
One extra X One extra
aaaXaaa
aa | a
aa aaaa aaa
a aaa aa
So now you'll notice you suddenly have an aaaa person
that can get split a number of ways and it sort of depends what the cross overs
on the chromosomes are like... the more repeats the more cross overs and the
more odd combinations you can get
so aaaa X aa
so possibilities of cross over events mean that you'll mostly get a split of
"aa" and "aa" but some "a" and "aaa" can also exist - the rate of cross over is
up to you and depends on the size of the repeat in base pairs... the longer the
size the more the crossover is likely to happen.... but often this is also a
vanishingly small number until you get into high numbers of repeats.
so the aaaa person produces aa | aa | a | aaa
and a normal person a aaa aaa aa aaaa
a aaa aaa aa aaaa
but the ratios aren't direct, more like 99.98% aaa 0.001% aa and 0.01% aaaa -
tho the actual amount of aa and aaaa you get from that would be smaller then
0.01% normally
but now cross an aaaa X aaaa
aa | aa | a | aaa
aa aaaa aaaa aaa aaaaa
aa aaaa aaaa aaa aaaaa
a aaa aaa aa aaaa
aaa aaaaa aaaaa aaaa aaaaaa
The aaaaaa person would be due to two crossover events in two different people
so it would be even smaller in frequency then the other, but still a
possibility.
keep going and see what sort of combinations you get with 20 repeats.... but
keep in mind as the number of repeats gets larger then the crossover events
become more frequent... and possibly weirder (like half repeats). Also at some
point this repeat is going to disrupt gene function entirely and it will stop
working... so you loose the trait, but if you married someone normal some of
your children could get the trait back (depending on the dynamics of the
break). Or you can declare that given a large enough repeat it causes other
chromosomal malfunctions and a 35+ repeat person can not have viable offspring
with a 2 repeat person; or a 35+ repeat person can not have viable offspring at
all.
So you'd need to pick some numbers for where you want your break overs to be,
what the frequency of cross overs are, and what size you want your repeat to
get to before it breaks completely (and acts like having no gene)....
mathematically IIRC this comes out as an odd bell curve skewed to most people
being completely normal or on the verge of having the problem but never
actually having it manifest because they marry people out of their community
without the genetic problem.
Cross over frequencies in areas where they occur a lot seem to be in the
frequency of 1 in 10^6 sperm in a male, according to one study.... so your
frequency's of cross over should be somewhere between 10 ^ -4 to 10 ^ -6 if the
gene is in a mutational hot spot. If it's in a very stable location in the DNA
then your cross over frequencies can be much much much smaller.
Environment can also play a part in crossover frequency... so an environment
that causes certain mutations (like what we do in mutational studies in plant
where we soak seeds in chemical mutagens) is going to increase the possibility
of weirdness.
-Sue
----- Original Message ----
From: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
To: The GURPSnet mailing list <[email protected]>
Sent: Monday, April 30, 2007 6:02:53 PM
Subject: Re: [gurps] Fake scientific genetics for Magery...
At 04:41 PM 4/30/2007 -0700, you wrote:
>Yeah, I'd go for epigentic effect too... but you pretty much can't
mathematically model that at all, what with the various combinations of
protiens interaction and mi/siRNA effects you can have with that. Not to
mention all the womb condition possibilities.
>
>But if Hal wants something that's a bit more mathematically calculable
then I'd go for a non-standard inheritance pattern - like the alzheimer's
or parkinson's where the condition gets more severe the more repeated
motifs you have. That way he can have incomplete penetrance effects; or
high break over conditions droping the number of mages in the population
even if it is a benifical mutation; or pretty much any bizzare numbers and
combinations he wants.
>With that type of model he can even get combinations of two magery 3
parents that have only mundane childern if after a certian number of
repeats the gene disfunctions entirely giving a mundane child who can only
have mundane childern.
>;)
>Basically
>0-10 repeats = normal functioning proteins
>10-20 repeats = magery 1 high activity protiens
>20-30 repeats = magery 2 super high activity proteins
>30-35 repeats = magery 3 mega high activity proteins
>35+ repeats = gene is broken - no active proteins because the number of
repeats is so large that it can't be read through.
>
>Usually these types of mutations are found in the promoter regions of a
gene - tho sometimes in introns... so they aren't mendelian in inheritance
pattern on top of all that, but I digress.
>The nice thing with this is that if the parents know the number of repeats
they had in their genetics (say in a shadowrun type universe) the break
down is mathematical and basically mendelian (sort of, there are always
exceptions)... you get weird punnett squares if you try to model it but you
can get them... where one person has 3 or more possiblities for the state
of a chromosome and the other has one or two (like a normal gene).
>-Sue
Ok, so how would it break down and what would be the math behind it (more
or less)? :)
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