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Louis Kessler's Behold Blog » Blog Entry           prev Prev   Next next

FamilyTreeDNA’s Chromosome Match File - Sat, 25 Jun 2016

My DMT (Double Match Triangulation) program that will make use of FamilyTreeDNA chromosome segment match data is nearing completion. As I was looking through some of the results it was producing, I got an unexpected surprise.

I found there were some people my uncle Harry matched to in his Chromosome Browser match file that were not among his Family Finder matches. I found out that:

The FamilyTreeDNA Family Finder information is different from their
Chromosome Match information

To make sure, I re-downloaded both the Family Finder matches and the Chromosome Match file for my uncle. My uncle had 7,777 people listed as matches in his Family Finder Match download (FFMD). In his Chromosome Match download (CMD), my uncle had 176,436 segment matches which were from 8,017 people.

There were 26 people whose names were listed twice in the FFMD. Many of them were two different people with the same name, but a few were the same people with two different tests done. But they were merged together in the CMD and their matches were combined into 26 single people. This is a mistake by FamilyTreeDNA that they should fix. Since my program uses the Chromosome Match download, the two kits will be treated as one for matching until this is fixed. (See my post: Misleading Double Entries in FamilyTreeDNA Data, which gives more information about this problem)

Also, the FFMD file downloads Unicode characters correctly, but the CMD file does not. So the CMD file does not display names that are written with accents or in a different script correctly and sometimes does not include the person at all. FamilyTreeDNA should fix this as well. There are 31 people in the CMD whose names do not display properly or who are not included in the FFMD file.

Then the people’s names in the CMD file have two spaces between their first name and last name. There should be only one space between their names, as in the FFMD file. Fix please.

The bigger question is why does the FFMD has 7,777 people versus the 8,017 in the CMD? That’s 240 people who are in the Chromosome Match file that are not listed in the Family Finder. These people all have significant cM matches. I don’t know why they are in the Chromosome Match file but don’t show up in Family Finder. My suspicion is that there is some criteria that is filtering them out of the Family Finder matches. I don’t know what that is. Maybe someone from FamilyTreeDNA should explain. Whatever the reason, the people listed in the Family Finder as matches should be the same as the people listed in the Chromosome Browser download, and FamilyTreeDNA should fix this.

Next problem. For the 7,777 matching people, the total cM for 660 of them in the CMD was at least 5 cM higher than what was given as the Shared cM in the FFMD.

So I picked a person at random who was among these 660. In FamilyFinder, my uncle has this match to Carole who shows up as having 47.70 Shared cM with Harry.

image

I then went to the Chromosome Browser, found Carole, and did the Download to Excel (CSV Format) that is the 1st Optional View at the top of the page. It gave the following:

image

Ah, I see. The difference is that the Family Finder shared cM don’t include the X chromosome cM. This is okay. Since the X chromosome is included in the Chromosome Match Download file, my program will be able to find and triangulate X matches as well.

So there are a few glitches in FamilyTreeDNA’s creation of the Chromosome Match Download file.  I have the above concerns (shown in red). If they get addressed by FamilyTreeDNA, it would help people like myself who want to make use of the file. If anyone reading this knows any of the technical people at FamilyTreeDNA, please let them know about this blog post. They can contact me if they want more explanation.

None-the-less, those aren’t show-stopping problems. My DMT program should still do a pretty good job analyzing the Chromosome Match Download file, despite its minor flaws.

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