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Archiver > GENEALOGY-DNA > 2008-05 > 1211119813
From: Beth Long <>
Subject: Re: [DNA] Y-DNA tEsting
Date: Sun, 18 May 2008 07:10:13 -0700 (PDT)
In-Reply-To: <BAY141-W9A305417A649965FC2495A3CA0@phx.gbl>
Hi Mitzi,
In Smith and Jones matches, you are talking about British Isles surnames (R1b probably), which will likely produce an inconclusive result at the 12-marker level. For example, my own surname (Moore) has a surname project, and results are so similar at the 12-marker level that it really does require 37 markers to identify the different lines. My uncle joined the project starting with 12 markers, but subsequently went to 67 when he saw the situation.
My understanding is that this is because the clades of R1b found in the British Isles are fairly young, plus there was a very rapid population growth in fairly recent times (since the middle ages). This results in a lot of very similar DNA.
In our project, we have a whole different history, and not much R1b. Our subject population appears to be dominated by "founder effect" (i.e. many people are descended from a relatively small group of individuals) The lines are readily definable using 12 markers.
A false positive means that there appears to be a match when there is not (so two people, regardless of surname, match at 12 markers, but the match "falls apart" at additional markers).
Likewise, there could be a false negative (two people match only 11/12 or even 10/12 can converge with additional markers).
The bottom line is that for a British Isles R1b project, 37 markers is likely to be needed to differentiate lines, but it would be a mistake to say that 12 markers are useless for projects with other populations and/or other haplogroups.
Beth Long
Mitzi* Bateman <> wrote:
>So lets say you are doing a Smith DNA project. You do the 12 marker test. >When you get your results, there are six exact matches. You look at the names >and including yourself, there are five Smiths and one Jones. ??
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