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Archiver > APG > 2006-04 > 1146101058


From: "robert mclaren" <>
Subject: Re: [APG] Mills DNA
Date: Wed, 26 Apr 2006 21:24:18 -0400


Ruy,

I don't disagree with what you said, but I would put in a caution in
reference to one comment -- that a 12-marker test can be used to disprove a
relationship. This is certainly true, but there is a grey area. I have seen
matches of 9/12 that are in the same family. In this case, the next 13
markers all matched and I think there was one
mismatch in the final 12.

The more results I see, the bigger the grey area gets!

Bob


> [Original Message]
> From: Ruy Cardoso <>
> To: <>
> Date: 4/26/2006 11:30:27 AM
> Subject: Re: [APG] Mills DNA
>
> There have been a few recent posts on Y-DNA testing,
> excerpted below.
>
> > wrote:
> >
> > I would also agree with Ms. Lustenberger's
> > assessment, and with the excellent explanation
> > added by Adam Bradford. There are estimates that
> > 12/12 matches are unreliable in up to 21% of such
> > matches,
> >
> > wrote:
> >
> > It's not that 12 markers isn't sufficient to
> > identify the individual testee's haplotype - a
> > haplotype is simply the values a person holds
> > on those 12 markers.
> >
> > Helen S. Ullmann wrote:
> > She was emphatic that a 12-marker test
> > really isn't sufficient to identify the haplotype.
>
> I have a few clarifying points to mention in response
> to the excerpts above, and I hope that they will not
> confuse things further. But let me give it a go.
>
> First, there is nothing that says a haplotype has to
> be defined in terms of 12 markers, though it is common
> to speak of them that way since 12-marker tests have
> been popular to date; in fact, they are still being
> used in the Genographic Project run by National
> Geographic. But you can just as easily speak in terms
> of a 27-marker haplotype or a 33-marker haplotype or
> whatever other number you like. Helen's comment
> referred to *the* haplotype, but such a concept
> doesn't really exist except in terms of a defined set
> of markers.
>
> Second, the more markers you consider, then the more
> haplotypes there can be. Taking things to an extreme,
> you might imagine a 1-marker haplotype. Depending on
> the marker being used, there might only be eight or
> nine different values that such a 1-marker haplotype
> could take on. But look at, say, 50 markers, and
> there could be millions or billions of combinations.
> In theory, there are far more combinations possible
> than there are people on Earth, but of course not
> every combination can show up in the population.
>
> Now brothers, for example, would likely have pretty
> similar 50-marker haplotypes, but even they might not
> be identical -- most of the markers would match but
> not necessarily all -- and the more markers being
> examined, the less likely you are to find a perfect
> match. This is actually a good thing, because if
> mutations *never* occurred, then there would be only
> one haplotype out there for any number of markers, and
> we would be deprived of a useful tool for sorting
> people into families.
>
> Third, the conventional wisdom is that a 12-marker
> test is not really useful to support a supposed
> genealogical relationship, but it may certainly be
> enough to disprove one. So the test continues to have
> some genealogical value, just not in the direction
> that people would prefer. Don't we all prefer to
> support hypothetical relationships than to disprove
> them?
>
> Finally, it is easy to confuse two similar terms,
> haplotype and haplogroup. A haplotype, as already
> noted above, is simply a combination of particular
> marker values, and of a particular type (STRs, or
> short tandem repeats). A haplogroup, on the other
> hand, is defined by a different type of mutation
> altogether (SNPs, or single nucleotide polymorphisms).
> While there is some dispute about the frequency with
> which the different types of mutations occur, there is
> no question that STR mutations, the kind most commonly
> discussed when talking about Y-DNA tests, happen far
> more often than SNP mutuations.
>
> In fact, SNP mutations are so rare that they aren't
> really useful for traditional genealogy at all (i.e.,
> for relationships over the past three or four hundred
> years). But they are very useful for determining more
> ancient origins. Now while one can test for SNP
> mutations directly, a lot of people try to determine
> possible relationships between particular STR marker
> values (or combinations of them) and particular SNP
> mutations; in other words, they want to use haplotypes
> as a clue in determining haplogroups. If you read the
> postings on the Genealogy-DNA mailing list at
> Rootsweb, I would say that the majority of posts are
> on this very topic.
>
> I hope that all helps people's understanding of Y-DNA
> testing, at least a little.
>
> Ruy Cardoso
>
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