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Archiver > GENEALOGY-DNA > 2012-03 > 1332389803


From: Jim Bartlett <>
Subject: Re: [DNA] Phasing 4th Cousins
Date: Thu, 22 Mar 2012 00:16:43 -0400
References: <4F6A49C2.5010505@yahoo.com> <REME20120321183300@alum.mit.edu><C77D5C96-82B9-4382-B733-ECDA769836DF@verizon.net><REME20120321215901@alum.mit.edu><6F17482E-20A6-461E-9B6D-B3E48E47A680@verizon.net><REME20120321233836@alum.mit.edu>
In-Reply-To: <REME20120321233836@alum.mit.edu>


John

I'm not worried about finding matches - I have 1,000 at 23&Me and 240 at FTDNA. So far 62 of them and I have agreed on Common Ancestors, only a few of whom are 5th cousins or less. The deal is that every match has at least one large segment - the companies believe most are IBD - and the number of cousins increases faster than the probability of one matching decreases. In other words, if our Trees were more complete, we'd find more matches beyond 6th cousins. I know the chance of one match is small, but since we have so many distant cousins, the chances of a hit are pretty good.

As more and more folks get atDNA tested, our quilts will fill in. So far I've only triangulated on two segments. But I now understand the process. And I'm not interested in completing the quilts, I'm interested in identifying road signs that point to specific ancestors.

Jim - Sent from my iPhone - FaceTime!

On Mar 21, 2012, at 11:40 PM, (John Chandler) wrote:

> Jim wrote:
>> Thanks - I'm thinking of a patchwork effort. In the end we have the
>> whole quilt. And I think we would wind up with 2 quilts - one for
>> maternal side and one for paternal side - and this would be true for
>> each person in our ancestry.
>
> In fact, our ancestors are bound up in pairs, and the quilts would be
> produced together as one batch of 4x22=88 for each pair. Those
> ancestors who had children by multiple spouses would entail larger
> batches.
>
>> If we limit this to large segments, known to be IBD (say over 10cM
>> each), the paternal/maternal quilts would have a lot of small holes.
>
> Consider: for even a pair of MRCA's just 6 generations back, the
> chances of sharing a segment that large with another descendant are
> something like 10%. It takes a lot of descendants to end up with
> more "quilt" than "hole".
>
> John Chandler

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