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From:
Subject: Re: [DNA] Comparing Ancestry Painting (23andme) to AncestralOrigins Genome B...
Date: Wed, 24 Mar 2010 05:35:28 EDT


FTDNA doesn't analyze biogeographic ancestry.

Lots of people on DNA-Forums have posted comparisons of 23andMe and
deCODEme. Virtually everyone who is reported as 100% European at 23andMe receives a
small percentage of Asian and African at deCODEme. This is due to the
different approaches taken for analyzing the same set of HapMap data. Both
companies analyze the chromosomes segment by segment. This is the big innovation
compared to DNA Print, which was based on a small number of Ancestry
Informative Markers scattered over the genome.

The main difficulty is that there are very few markers that are 100%
informative (found in everyone in one population and no one in other populations).
For each segment, deCODEme will assign a probability to the origin, say a
7% probability that the segment is of Asian origin and 4% of African origin.
23andMe reasons that a small segment is unlikely to be composed of three
different origins, so it picks the one or two most likely origins (since you
have two parents).

23andMe results seem to be sensible for people with documented admixture

http://spittoon.23andme.com/2008/06/13/a-beautiful-ancestry-painting/

or for people where admixture is plausible based on the population history
(e.g. Puerto Ricans tend to show all three components). For most cases I've
seen, if the 23andMe painting does show admixture, deCODEme will also
recognize the same segments. However, it seems to me that the deCODEme percentages
for 23andMe's 100% Europeans are so similar for everyone across the board
that they are hardly informative about an individual's ancestry.

One last point -- deCODEme is apparently doing Monte Carlo simulations, so
some people who uploaded their 23andMe results multiple times got different
answers on each run.

Ann Turner
Disclosure: I have a consulting arrangement with 23andMe, but the
statements expressed above are my own and not official policy of 23andMe.

In a message dated 3/23/2010 8:38:20 PM Pacific Daylight Time,
writes:

> Does anyone have results from all three autosomal tests: 23andme,
> decodeme, and FTDNA? Any differences in biogeographic ancestry
> between the tests?


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