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Archiver > GENEALOGY-DNA > 2008-05 > 1211129798


From: "Alister John Marsh" <>
Subject: Re: [DNA] Y-DNA tEsting- what constitutes "match".
Date: Mon, 19 May 2008 04:56:38 +1200
References: <c89.29fc87ee.3561a304@aol.com>
In-Reply-To: <c89.29fc87ee.3561a304@aol.com>


I sometimes feel that different people have different standards for judging
what "match at 12 markers" and "don't hold up at 25 markers" mean.

I tend to think that a 12/12 match, where both are exactly AMH, for
practical purposes should not be treated as a significant match. On the
other hand, if two haplotypes have in common 2 or 3 unusual off modal marker
scores in the first 12 markers, I would be looking at 10/12 or even 9/12 as
having potential to be related. In one group I have two persons with 4
mutation steps difference at 12 markers, who matched on a distinctive family
marker, who in the context of the wider picture, I considered likely part of
the same family. At 37 markers when they were later obtained, bearing in
mind a range of distinctive family markers, they look well and truly related
to me.

It is a bit simplistic to say 10/12 is or isn't a match, or 4 mutations
difference on 12 markers isn't a match, without looking at distinctive
family markers, and then looking at those two haplotypes in a wider context.

At 6 mutation steps on 25 markers, there is realistic statistical
possibility of them being related since surnames. Are people saying that 6
mutations steps on 25 markers is a match "falling apart"? Perhaps it is
just a recLOH or some such event? Perhaps testing 67 markers would reveal
more? I think if at 25 markers, it can't be realistically discounted that
they are related since surnames, then it is premature to say it is not a
match, or the match has fallen apart.

In one past situation, I had if I recall correctly only 2 markers
overlapping between different marker sets tested by different persons. One
of those markers was very unusual, and distinctive to a particular family.
On the basis of that 2/2 match, which included a very distinctive marker
score, and surname in common, I tentatively linked them as part of the same
group. When they had tested more markers in common they had a very strong
match.

It is simplistic to judge "match" or "match falling apart at 25 markers" on
just the number of mutation steps difference. Context is very important.

The larger surname projects become, the better the context is for comparing
two haplotypes. Two haplotypes compared in isolation, by someone not
experienced in interpreting DNA results, could be very misleading. The
added value of experience of the interpreter, is often even able to pick
"lab errors" in results.

John.

-----Original Message-----
From:
[mailto:] On Behalf Of
Sent: Monday, May 19, 2008 3:20 AM
To:
Subject: Re: [DNA] Y-DNA tEsting


In a message dated 5/18/2008 3:57:16 A.M. Central Daylight Time,
writes:

Both my Clark, Smith, and Brown cousins have 12/12 matches with the same
surname that do not hold up at 25 markers.



So those particular 12/12 matches are considered false positives?


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