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  #1  
Old 12th March 2013, 09:40 AM
jbarry6899 jbarry6899 is online now
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Thirty Matches on One Segment

I was killing time waiting for my FF results to reappear, so I was recently analyzing my DNA matches on gedmatch.com and found a surprising result. It appears that I am among 30 individuals who share a matching segment on chromosome 1. In all cases, this segment starts at position 742,429. It terminates between 3,103,540 and 3,644,607. Some of us also share shorter matching segments and we are predicted to be related within 5-7.1 generations. Very few have provided any family information. Of those who did, most were of Irish origin but there were people with Russian, Polish and Finnish surnames.

I've emailed all of these people this morning to see if we can find any common ancestors or locations. About 1/3 of the emails were rejected for one reason or another but perhaps I will get some responses. Hoping at least some are IBD.

I was wondering how unusual this is. Have others found that number of matches with the same starting position and size?

Thoughts welcome,

Jim
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Old 12th March 2013, 10:36 AM
Frederator Frederator is offline
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That's interesting.

Have you noticed how many cM and SNP's are in play, on average?

Is there a meaningful pattern in how they match one another? Perhaps some are from the maternal chromo, and the others on the paternal, and the 'overlap' is only apparent but not real?
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Old 12th March 2013, 11:11 AM
boi568 boi568 is offline
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I have one of those situations, on Chromosome 20, and I can trace it through my mother. Only it's more like 50+ matches in the same stretch. Build 37 reduced the cM length from about 17 to more like 13 or 14, but my sense is that this is not a close set of relatives. I was surprised Build 37 didn't reduce it much more.
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Old 12th March 2013, 11:27 AM
jbarry6899 jbarry6899 is online now
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Thirty Matches on One Segment

My parents are not living and I can't phase the results. The matches range from 8 to 9.5 cM; I didn't copy the number of SNPS.

I've heard from one person and he has an Ulster ancestor who is also in the tree of one of my Ancestry.com distant cousin matches. There are two other people in my gedmatch list who claimed Ulster ancestry, so that's my guess for now.

I'm sure some, if not most, of these matches are IBS but any true matches could be interesting.

Jim
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Old 12th March 2013, 11:34 AM
madman madman is offline
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Quote:
Originally Posted by boi568 View Post
cM length from about 17 to more like 13 or 14
This is a 7th Cousin
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  #6  
Old 12th March 2013, 11:37 AM
boi568 boi568 is offline
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Quote:
Originally Posted by madman View Post
This is a 7th Cousin
I believe it, but that ancestor must have an unbelievable number of descendants to create that many matches in the same place.
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Old 12th March 2013, 12:12 PM
1_mke 1_mke is offline
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I'm starting to think some segments are "sticky". I have many examples in my own DNA and have heard of many others as well. I have absolutely no clue how or why that might work though.
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Old 12th March 2013, 12:16 PM
boi568 boi568 is offline
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Quote:
Originally Posted by 1_mke View Post
I'm starting to think some segments are "sticky". I have many examples in my own DNA and have heard of many others as well. I have absolutely no clue how or why that might work though.
The thing about a "sticky" segment is that it is probably overestimated in terms of cM. That is, the current Build gives it greater length than it deserves. If cM equalizes segments, no one segment should be "stickier" than another one.
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Old 12th March 2013, 01:02 PM
1_mke 1_mke is offline
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How about a 30.5 cM match on chromosome 9 that spans three generations in one line and two generations in another with only one other segment match as large as 5 cM and that being a single segment match in the two earliest generations?

My brother only got 18.4 cM of this segment match so it isn't completely persistent.
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  #10  
Old 12th March 2013, 06:00 PM
jbarry6899 jbarry6899 is online now
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Thirty Matches on One Segment

I have a little more information after corresponding with several of the matches and looking more deeply at some of the trees.

The number of SNPs on the shared segments is relatively small, ranging from 500-600.

With one exception, everyone who has responded, or who has a family tree online, has ancestors who left Northern Ireland early in the 18th century and settled in Pennsylvania or Virginia and then moved down the Appalachians and beyond.

I also have literally hundreds of matches on Ancestry DNA with people who come from similar family backgrounds.

My own family has Northern Ireland roots on 5/16 lines, but they stayed there or went to Scotland and didn't come to America until the 19th century.

My tentative conclusion is that there are some valid matches in this group but that they are much farther back than the calculators indicate, probably on the order of 8-10 generations or more. They appear to result from a small "sticky" segment that originated with a common ancestor in Northern Ireland in the 17th century or even earlier and was passed down through multiple family lines to their descendants today.

Any other thoughts welcome.

Jim
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