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Archiver > GENEALOGY-DNA > 2006-04 > 1145722242


From: "Ken Nordtvedt" <>
Subject: Re: Mutations (was [DNA] Genealogy as we knew it)
Date: Sat, 22 Apr 2006 10:10:42 -0600
References: <000201c66623$7d94a560$6601a8c0@DH870341>


----- Original Message -----
From: "Michael L. Hébert" <>
To: <>
Sent: Saturday, April 22, 2006 9:43 AM
Subject: RE: Mutations (was [DNA] Genealogy as we knew it)


> Interesting. Thanks for the numbers and explanation. I guess the dna is
> a
> little more stable than I had thought. So, regarding SNPs, are you saying
> that going base pair by base pair on the Y chromosome (excluding the
> recombining part), only one mutation in one base pair occurs on average
> per
> father/son transmission?

[Yes, on average there is probably a SNP mutation somewhere in all the base
pairs a mutation every father/son transition, or every second
transition..... This is all ball park estimation based on present knowledge
of typical SNP mutation rate and number of base pair sites. This also means
that a decent fraction of the time there might be two SNP mutations in the
same father/son transition, etc.

If there are 200 STRs in our ydna and each had an average of 15 repeats,
that's 3000 base pairs --- a drop in the bucket of all base pairs. But it
could happen, and it would affect the STR reading. If the SNP mutation
falls in the part of the dna chain close on either side of the STR where the
primers match on, it could render the primers inoperative I believe.

As we discover more and more SNP mutations and place them in the Tree, the
chances of seeing an SNP mutation in the past mutate again and define
another more recent branch will increase. This has been seen a couple times
already in the present Tree. R1a is a good example. The very low mutation
rate for SNPs compared to STR rates is what has kept this rare so far.

There is or should be, if nature's wise, correction machinery which notices
and corrects some mutations. For the important operative genes I would
think some strategy and configurations exist which lead to extra stability.
Whether that operates in the part of the ydna which is not supposed to code
for anything important, I don't know.

mtDNA has hyper variable regions and coding regions with different levels of
mutation rate. ]



Can an SNP occur at any base pair (even inside an
> STR) or are there sections of dna that are absolutely unchangeable? I've
> wondered how some SNPs that define the upper levels of the haplo tree
> (such
> as the ones that define the BR Hg) have remained so stable for so long
> throughout such large populations. Are they, for whatever reason, just
> more
> stable areas of dna than other areas?


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