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Archiver > GENEALOGY-DNA > 2010-02 > 1266107126


From: "Ken Nordtvedt" <>
Subject: Re: [DNA] Y Tree STR Mutations can not be counted
Date: Sat, 13 Feb 2010 17:25:26 -0700
References: <CE3717A90A0846309FF45B9117D7242D@PC>


----- Original Message -----
From: "Lancaster-Boon" <>

> So the real discussion should be about HOW AND WHEN you can be sure that
> the
> chance of things like back mutations and parallel mutations are small, and
> how much their possible existence in any set of haplotypes is affecting
> your
> confidence interval.
>
> I think this is Ken's point,


Andrew,

That's not my main point. Trees from founder to present sample of
haplotypes quickly acquire sufficient father/son transition events within
themselves, that the fast and medium speed STRs certainly have mutated
multiple times in the tree. And there is not a one to one correspondence
between the number of occurrences of such STR mutations in the tree and
number of final sample haplotypes showing a change or GD at the considered
STRs. Every node downstream of an STR's mutation in the tree enlarges the
number of final haplotypes showing the change (GD) at that STR. This is
even before you concern yourself whether there are back mutations, etc.

So again, even after having estimated the time depth of the tree in
generations, there is no way to evaluate the statistical confidence interval
of that age estimate without knowing the tree structure through its whole
history. The number of mutations occuring in each of the haplotype lines
back to the founder are not independent of each other; they share more or
less of their lines with each other depending on whether the haplotypes are
close or distant relatives, respectively. And the degree to which different
haplotypes share part of their ancestral lines with each other depends on
the tree structure through all the tree's history.

If by "parallel mutations" you mean multiple occurrences of an STR's
mutation in the tree, the estimate of when that becomes likely is
straightforward. Estimate the number of father/son transitions in total the
tree has on all branch segments, and multiply that number of mutational
opportunities by the STR's mutation rate.

For instance; if a tree has 1200 father/son transitions in it, and a marker
has mutation rate of 1/200, the expected or average number of times that STR
will mutate in the tree is 6, but it could be more or less with the
statistical distribution known; and similarly for every other STR. And
where in the tree those six or so mutations happen for the STR is also
random and unknown to us.



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