Archiver > GENEALOGY-DNA > 2010-11 > 1290997101

From: "Tim Janzen" <>
Subject: Re: [DNA] Provenance of a DNA segment (importance ofphasedhaplotypes)
Date: Sun, 28 Nov 2010 18:18:21 -0800

Dear Kathy,
There aren't easy answers to all of your questions.

I think that we do these autosomal tests for two primary reasons:
1. To confirm what we think is true. In other words to make sure that
there aren't NPEs in the lineages that we think are true by testing various
relatives and comparing their results to our own.
2. To break through genealogical brick walls. I think that targeted
testing is one of the most important ways that people should be using these
autosomal tests. For instance, I am currently trying to track down a
descendent John Reeves (b. ca 1745)(see
) for autosomal testing because I would like to see if there are matching
IBD segments with descendents of Jacob Youngman (b. ca 1825) because I
believe that his mother Elisabeth Reeves was probably a descendent of John
Reeves. If I find a significant number of matching segments then this will
help support the theory that there is a genealogical link.

There are clearly situations where people don't reach the 5 cM
threshold that seem highly likely to be genealogically related to other
people. One example I recently found is Robert Paine, who has two matching
IBD segments in common with my mother Betty Janzen and her brother Robert
Youngman. These segments are only 4.66 and 4.87 cMs in length, but each has
a relatively high number of SNPs for the segment (over 1000 SNPs for each
segment), which to me suggests that they are genealogically significant.
Robert Paine has early New England ancestry and shares at least several
ancestors in common with my mother in the 1600s.

Tim Janzen

-----Original Message-----
[mailto:] On Behalf Of Kathy Johnston
Sent: Sunday, November 28, 2010 11:56 AM
Subject: Re: [DNA] Provenance of a DNA segment (importance of

Do you think that Family Finder is tolerating too many mismatches? Are
genotyping errors and microdeletions major sources of false positives? If
these were not tolerated, then would there be way too many false negatives?

According to Bruce Walsh, the odds of a run of 5 cM being shared between two
individuals (when using 500,000 markers) is 1 in 10 million, but FF does not
use 5 cm as the threshold. It looks like 7.7 cM is the initial threshold
FTDNA is using. When they report on a match of 5 cm, are you saying that
they are ignoring important mismatches? It seems to me that the genotyping
errors and microdeletions may be a significant source of kinship prediction
errors. Should the technology be improved in order for it to really be ready
for prime time? Are our own natural deletions getting in the way of

Bennett Greenspan stated that FTDNA really only predicts 3 generations with
confidence. For most of us, we already know 3 generations with confidence,
so why do the test? I think that both FF and RF have come up with matches
that can be confirmed quite well at the 4th cousin and below level.


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