Archiver > GENEALOGY-DNA > 2013-03 > 1362521789

From: Jim Bartlett <>
Subject: Re: [DNA] Finding common ancestor between three people
Date: Tue, 05 Mar 2013 17:16:29 -0500
References: <03d401ce19d0$4c42eef0$e4c8ccd0$><007901ce19d5$991e6ec0$cb5b4c40$@net>
In-Reply-To: <007901ce19d5$991e6ec0$cb5b4c40$@net>


Wouldn't Triangulation be another way to confirm this? If 2 or 3 or 4 folks all overlapped on the same shared segment and had the same Common Ancestor, I'd be pretty confident of mapping that segment - and knowing which parent passed the segment down.

Also my parents are 8th cousins, both descending from Sion HILL. I have several shared segments with Sion as the Common Ancestor. And in one case, I have a Common Ancestor on one of Sion's descendants with a 6th cousin - so I know which parent/side provided the segment.

As I fill up the map, even with distant cousins, I've found a few cases where it has become apparent that, although we have a Common Ancestor, that ancestor is the one who provided the shared segment, because other evidence indicates the Common Ancestor has to be with the other parent. But in most cases, other distant cousins have confirmed the Common Ancestor on that segment.

Jim - Sent from my iPhone - FaceTime!

On Mar 5, 2013, at 2:14 PM, "Tim Janzen" <> wrote:

> In order to determine if a IBD segment came down through your
> paternal side or your maternal side you have to do chromosome mapping using
> known first, 2nd, and 3rd cousins. There is no substitute for this.
> Otherwise, you are simply guessing if the ancestor is known to have occurred
> on both sides of your family tree. Let's say that a first cousin of yours
> on your paternal side also shared the same segment with your two matches.
> This would indicate to you that the shared segment was passed down through
> the paternal line of descent from the known ancestor. If you haven't
> previously studied my mom's chromosome map at
> %20Janzen%20(public).zip I suggest that you do so before trying to
> understand the details of chromosome mapping.
> Sincerely,
> Tim Janzen

This thread: