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Archiver > GENEALOGY-DNA > 2002-08 > 1030672760
From:
Subject: Re: [DNA] How Specific is 12 marker test
Date: Thu, 29 Aug 2002 18:59:24 -0700 (PDT)
I wonder if your results would be the same between AMH
and non AMH subjects.
On Wed, 28 August 2002, lmpajg wrote:
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> Over the last few weeks, there has been a lot of
> discussion on this list =
> about the value of running a Y-chromosome surname
study
> with a smaller nu=
> mber of markers before deciding on an upgrade to a
> larger set of markers =
> if testees match. FamilyTree DNA offers a less
> expensive test at 12 loci=
> , followed by an optional upgrade to 25 loci at an
> additional price. Upg=
> rading to a larger set of markers provides a shorter
> estimated time to mo=
> st recent common ancestor (MRCA) for subjects who
match
> closely, but it a=
> lso carries a higher probability of not matching as
> well on all additiona=
> l markers. Some members of this list believe that a
> smaller set of 12 ma=
> rkers are "next to worthless" in sorting
out family
> relationships, while =
> others have stated that 12 markers worked fine for
> their studies. =20
>
> I decided to look at this question numerically, using
> the evidence from t=
> he surname studies to date that have 25-marker
results:
> what became of t=
> he 12-marker matches when expanded to 25 markers?
>
> Data here are from the 16 surname studies on Chris
> Pomeroy's and Kevin Du=
> erinck's lists of Y-chromosome surname studies which
> had posted on the we=
> b detailed results of 25-marker tests for at least two
> individuals as of =
> August 15, 2002. Excluded were a number of studies
> with only one testee =
> reporting 25-marker results so far, and many others
> with studies in progr=
> ess but no results posted yet. The 16 studies covered
> here include 154 i=
> ndividuals tested on 25 loci, in addition to 186
> subjects with only 12-lo=
> ci results posted. =20
>
> Since many of these testees made a conscious upgrade
> from 12 to 25 marker=
> s, there's a built-in bias to high initial matches in
> this set - more 12/=
> 12 and 11/12 matches than you would probably find on
> average in a surname=
> study. However, not all of these 154 individuals had
> gone through a two=
> -step process of testing 12 markers first, then
> upgrading to 25 if their =
> matches were close - some surname studies had some or
> all of their partic=
> ipants tested initially at all 25 loci. For these, I
> tallied results bas=
> ed on the subset of 12 markers as well as on the whole
> 25. All compariso=
> ns were made strictly between individuals within a
> surname study - no com=
> parisons of individuals across studies. And to limit
> the number of pairw=
> ise comparisons, I selected the best match for each
> individual based on h=
> is 25-loci results, then tabulated where his 12-loci
> results would have p=
> laced the match. The work was greatly simplified by
> the fact that most s=
> urname study coordinators have presented their results
> grouped by strengt=
> h of the match.
>
> Results are as follows: =20
>
> Overall most of the matches found to be "close
> relatives" at 12 markers t=
> urned out to be still close at 25 markers - defining
> "close relatives" as=
> matching at least 11 out of 12 markers or on at least
> 23 out of 25 marke=
> rs. But weaker matches, especially at 9 or fewer out
> of 12 markers, were=
> even weaker at 25 markers:=20
>
> Matches----------------Matches out of
> 25--------------------Row
> out of 12____25__24__23__22__21__20 or fewer___Total
>
> __12_______60*_15___3___1___2_____9_________90
> __11_______na__15___5___3___1_____3_________27
> __10_______na__na___1___0___1_____2__________4
> 9 or fewer___na__na__na___0___2____31_________33
>
> Col .Total___60__30___9___4___6____45________154
>
> * Ex: '60 of the 90 matches at 12 out of 12 markers
> also matched at 25 o=
> ut of 25'
>
>
> Rounding the results off to simple numbers, and on the
> conservative side,=
> =20
>
> * For matches at 12/12 markers, in more than 4 out of
> every 5 cases (78/9=
> 0), the relationship still remains close, at least a
> 23/25 match, if 25 m=
> arkers are tested
> * For matches at 11/12 markers, in more than 2 out of
> every 3 cases (20/2=
> 7), the relationship holds to at least a 23/25 match.
> * For matches at 10/12 markers, only 1 out of 4
reached
> a 23/25 match; mo=
> st were at 21/25 or fewer.
> * For matches at only 9 or fewer markers, the best
> accomplished was a 21/=
> 25 match; most were at 20/25 or fewer.
>
> These results show that 12 markers can take you quite
a
> ways in sorting o=
> ut relationships - definitely 12 are enough to
separate
> out cases who are=
> not closely related (the cases of 9/12 or fewer
> matches), or to suggest =
> that a relationship may be borderline (the 10/12
cases,
> if not otherwise =
> supported). As others on the list have noted, 12
> markers are definitely=
> enough to sort out people who *don't* connect. =20
>
> On the other end of the spectrum, if a match is 11/12
> or 12/12, these dat=
> a suggest that the majority of these individuals will
> remain closely rela=
> ted even at the shorter time to MRCA that 25 markers
> provide. In fact, w=
> ell over half of those who had zero or only one
> mutations between them on=
> 12 markers remained at the same zero or one mutation
> on all 25 markers (=
> cases on the diagonal in the matrix above). Finding
> such a relationship =
> at the lower price for a 12-marker test sounds very
> attractive. But the =
> exceptions are sobering - about 1 out of every 5
> perfect 12/12 matches an=
> d about 1 out of every 3 of the 11/12 matches would
not
> turn out to be cl=
> ose relations at all after testing at 25 loci. To
> clarify these matches=
> , a larger set of loci was essential. =20
>
> I would be interested in hearing what other list
> members think about thes=
> e results. I personally was surprised that the
> additional marker upgrade=
> didn't lead to even finer discrimination among cases
-
> more people staye=
> d "closely related" at the 25-marker step
than I might
> have expected befo=
> re looking at the data. (Perhaps it was just good
> old-fashioned paper ge=
> nealogy work that helped these testees make good
> decisions on who/when to=
> upgrade?) =20
>
> Thanks to all those who have made their numerical
> results available on th=
> e web for exercises such as this.
>
> Julie=20
>
>
>
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