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View Full Version : Strange Gedmatch behavior



soulblighter
05-31-2013, 04:45 AM
I noticed two new matches on Gedmatch: Lets call them Sample A and B.

One to One comparison between My sample and Sample A


Chr Start Location End Location Centimorgans (cM) SNPs
18 6,553,297 8,495,193 9.2 694

Largest segment = 9.2 cM
Total of segments > 5 cM = 9.2 cM
Estimated number of generations to MRCA = 6.1

One to One comparison between my sample and Sample B



Chr Start Location End Location Centimorgans (cM) SNPs
18 6,710,798 8,543,598 8.6 663

Largest segment = 8.6 cM
Total of segments > 5 cM = 8.6 cM
Estimated number of generations to MRCA = 6.8

One to One comparison between sample A and Sample b

Largest segment = 0.0 cM
Total of segments > 5 cM = 0.0 cM
No shared DNA segments found

One to One comparison between Smaple A and my Mom, and Sample B and my mom:
Neither Sample A nor Sample B share any segments with my Mom.

How is it possible, that I share a large segment on the same chromosome, around the same region with both of them, while they dont share any with each other or with my mom?

AJL
05-31-2013, 05:19 AM
One possibility is that both are related to you through your father, but that their matches with each other are under threshold, and a few SNPs from your mother are extending the run of DNA in contrary directions in the two cases.

soulblighter
05-31-2013, 09:07 PM
One possibility is that both are related to you through your father, but that their matches with each other are under threshold, and a few SNPs from your mother are extending the run of DNA in contrary directions in the two cases.

I think it is a bug in Gedmatch.

I have two samples uploaded on gedmatch. One a combined dataset(F2 and V3) and another an FTDNA dataset(F2).

One of the samples has a 9cM segment match with my FTDNA dataset at Chromosome 18, but none with my combined dataset!

AJL
05-31-2013, 11:25 PM
Weird! Sounds like it could be a bug.

Claxon
06-06-2013, 11:59 PM
I just uploaded my FtDNA and 23AndMe data to Gedmatch. All Chr agree, except 7
462
why would they disagree
clarification please ?
Rich

AJL
06-07-2013, 03:44 AM
I just uploaded my FtDNA and 23AndMe data to Gedmatch. All Chr agree, except 7
462
why would they disagree
clarification please ?
Rich

Possibly different tolerances of non-matches (somatic mutations, errors in calls, etc.)?

Claxon
06-07-2013, 09:22 AM
Possibly different tolerances of non-matches (somatic mutations, errors in calls, etc.)?

I did attach a snip of the Chromosome, but it is not showing up on my original post.

I am getting different people on the Family Finder to the Relative Finder, and wonder if this could be the reason.

Gedmatch shows my FtDNA and 23 data as one generation different also.463

AJL
06-07-2013, 01:15 PM
^ I think the generational difference is probably easier to account for -- it might just be a different algorithm they use.