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Archiver > GENEALOGY-DNA > 2007-03 > 1173924912


From: "Alfred A. Aburto Jr." <>
Subject: Re: [DNA] OmniPop caution received from FamilyTreeDNA
Date: Wed, 14 Mar 2007 19:14:48 -0800
References: <BAY121-F33C19B1858077C537B5B85B5720@phx.gbl>
In-Reply-To: <BAY121-F33C19B1858077C537B5B85B5720@phx.gbl>


Thank you John & Jim. I see now how an excess of admixture can make the
OmniPop, etc., results very ambiguous!
Al

> Jim Pearsall wrote:

>----Original Message Follows----
>From: (John Chandler)
>
>Al wrote:
> > Where is the fault with the method?
>
>We discussed this a bit last time. The numbers that come out of any
>of these population comparisons are simply probabilities (or
>reciprocals of probabilities) that a member of the population in
>question would have the stated genotype. There is nothing about
>cross-bred individuals, mostly because such individuals do not
>generally exist in enough numbers to constitute a recognized
>population of their own. The important point here is that "high"
>numbers for two separate populations cannot be interpreted as an
>indication of admixture of those populations in the test subject, and
>there are no numbers for comparison for the hypothetical mixed
>populations, and so you can't say *anything* about someone of mixed
>ancestry with this method (unless he or she happens to belong to a
>mixed population that *is* included in the database).
>
>Note: hypothetical mixed populations can easily be simulated, but
>the correction factor for population size is all the more important
>for such "fakes" and is uniformly "roughly zero" for all such.
>
>John Chandler
>
>
>John,
>
>My example maybe the more "exotic," but looking through OmniPop's list of
>about 200 populations and based on my own experience, I can conclude that
>the tool is interesting for forensics, but has significant limits.
>
>As you allude, it is best suited to relating an individual of ONE particular
>population to a list of known populations with corresponding probabilities.
>I tested this with a CODIS marker values I know belongs to a contact from an
>ISOLATED population. OmniPop worked well in this situation.
>
>However, looking back at my own family history, and probably similar to many
>American families; we can trace our lines to many different populations from
>around the world, be it in different ratios... e.g. English, Irish, Scot,
>French, German, Swedish, Italian, Russian, Jewish, many different
>populations in Africa, many different populations in Asia, etc...
>
>What if an individual has grandparents that are: Irish, Italian, German, and
>French? For the forensic anthropologist, how will they know if a particular
>DNA sample is from a person of ONE particular population, or a person of
>MIXED heritage prior to running the tool?
>
>OmniPop has the clever solution of having both "super-populations" as well
>as "sub-populations." A "super-population" maybe like "FBI Caucasian" or
>"FBI African-American" and "sub-populations" being "Virginia
>African-American" or "New York African-American."
>
>Still, the testee needs to belong to ONE population to work well. If not,
>it may result in a stastical rank-list that has no relevance for the
>genealogist/researcher that is trying to find more clues...
>
>
>Jim
>
>

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