Recently, I shared with you an announcement by Family Tree DNA about the expected update to their Family Finder autosomal DNA product.
Family Tree DNA sent an e-mail to their project administrators yesterday evening providing additional information about their update that will be following shortly.
Their verbiage follows, but this additional information removed some question about how matches will occur. Some people, me among them, were concerned that the new matching algorithm would remove all matches below 9cM. This would happen if the new algorithm replaced the old one. I’m very pleased to report that’s NOT the case. This new algorithm has been implemented in addition to the old one that required 20cM and 7.69 cM or greater longest single segment.
If you don’t match utilizing the old algorithm, you get second chance now with the new one that has no total cM requirement and a minimum segment length of 9cM. If you match either way, that person will be on your match list. Blaine Bettinger created a handy-dandy flow chart showing this process.
The good news is that the old threshold will preserve your old matches and the new threshold will allow new matches that do have a 9cM segment or longer but don’t happen to have 20cM total. I think this is win/win – and a very welcome change
Family Tree DNA has refined their matching algorithm somewhat, but the net effect of this should be that people will have more matches, but no new matches under 9cM and few losses, unless it’s from the algorithm tweaking.
As you look at your new matches, also keep in mind that some of your new matches may simply be because people tested and their results just happened to come back during this time – so if you do see a match under 9cM that’s new – this could be why. It may not be a result of the change, just a function of timing.
Those of you with Jewish heritage that were worried about being overwhelmed with matches, you can worry a little less. Family Tree DNA has maintained their proprietary routines that attempt to minimize the noise in Jewish matches.
Here’s the meat of what Family Tree DNA sent to the group administrators:
After months of research and testing, we’re implementing those changes as soon as the quality assurance process is complete, which should be within the next few days.
Until now the amount of shared DNA required for two people to show as a match was a minimum of 20 total centiMorgans of shared DNA with a minimum longest block of at least 7.69 cM for 99% of testers, 5.5 cM for the other one percent. With the adjustment, if two people share a segment of 9 cM or more, they will show as a match regardless of the number of total shared cM. However, if there’s not a block that’s 9 cM or greater, the minimum of 20 shared cM with a longest block of 7.69 cM applies.
We also slightly altered other proprietary portions of the matching algorithm that will, to a small degree, affect block sizes and total shared centiMorgans. These changes should have only marginal effects, if any, on relationships, generally in the distant to remote ranges.
There’s a separate proprietary formula that is also applied to those with Ashkenazi heritage, but you can, of course, expect to have more new matches than those not of Ashkenazi heritage.
The entire existing database has been rerun using the new matching criteria, and all new matches have been calculated with the new thresholds.
Please keep in mind this change will not affect close matches, only distant and speculative ones. Some matches will fall off, others will be added. Most people will likely have a net gain of matches.
Your myOrigins results may change slightly with the rerun, but we have not updated or changed myOrigins yet. We’ll let you know when that happens.
And that’s not the only good news we have!
Some of you may have dealt with mtDNA results that had some issues with genetic distance. The fix for the root cause of that problem was released awhile back, but we had to wait until all the hardware installations were complete and integrated before re-running those kits affected prior to that fix. We’re in the process of deploying that update now!
Over the next few days, those affected will likely see differences in genetic distance of some matches as the corrections are implemented. Those who have tested after the fix whose mutations were correct may see an increase in matches to existing testers. That’s to be expected.
Thank you for your patience through the process.