01 November 2008

Why Test 67 Markers?

People who wish to test their Ydna often ask which test its best. First you have to determine what your goal is and then find the test that best meets it.

As genealogists, we want our test to further our research; therefore, it is imperative that the test be helpful within a genealogical time frame. The following numbers of markers that are tested give results which are and are not within genealogical time. Although the following are the tests provided by Family Tree DNA, any testing company using about that number of markers will produce a similar result. However, note that at this time, no other company tests 67 markers on the Y chromosome, except Family Tree DNA.

Thus chart indicates the time frame for a match within a set of markers.

DNA TMRCA (Time to the Most Recent Common Ancestor) and Probability to the Most Recent Common Ancestor (MRCA)

12 marker Ydna test tells you only about your most ancient ancestry....over 600 yrs ago and before surnames. The Genographic Project uses only the 12 marker for males as they are only interested in tracking the migration pattern of our most ancient ancestors. Their project is an anthropological study; not a genealogical one, but in time their data will help us.

25 marker match gives you a 95% probability of having a common ancestor within the last 600 yrs.

37 marker match gives you a 95% probability of having a common ancestor within the last 300 yrs.

67 marker match gives you a 95% probability of having a common ancestor within the last 150-200 yrs.

This means that the 37 marker and the 67 marker are the genealogists’ best choices as they fall withing a genealogical time frame. Prior to 600 years ago some cultures did not establish surnames. Actually, the Irish were probably the oldest culture and they began around 1000 years ago. However, the Welsh, the Jews and many others hae only had surnames for the last few hundred hears..

Although one can order the lesser number of markers (37) and upgrade at any time to a 67 marker test, the cost is a bit more than the difference between the two. There are also good reasons to update to a 67 marker and, in cases, reasons not to bother, at least until it is necessary.

So why upgrade to a 67 marker?

The following information will help the tester determine if a 67 marker is important to your goals.

It is important to know that a Ydna 67 marker test can:

* further refine the estimate of how closely related two individuals are.

* help groups of related testers find mutations which identify sub-branches in the family.

The following scenarios are good reasons to upgrade to a 67 marker:

If you are a member of a group of closely related testers with a good 37 marker match, but there is no paper trial to connect the croup, it may be wise to upgrade as:

* More mutations can result, giving you the opportunity to further subdivide the large group and look for more recent common ancestors.
(See Talley Project at www.familytreedna.com/puiblic/Talley-Tally)

If you are a member of a group with many mutations (more than the usually number…i.e., more than 3 with a 37 marker) and you think you are closely related with the paper trail.

* The marker increase may not increase the mutations.

* The marker mutations may increase, pushing the common ancestor too far away from the group.

* The marker mutations may help bridge the mutations within the group. Often this happens when you find a family who has many mutations and the paper trail supports a good connection. Some families do mutate more often than others. Finding more testers for the family may bridge the gap between those who have greater genetic differences. A 67 marker may also show the testers re closely related as the markers from 38-67 have few to no mutations. The more markers tested the greater number of genetic differences can be accepted for still being a close relationship.


Probability for Most Recent Common Ancestor

The following times back to the MRCA when ALL the markers match are based in the latest results of the mutation rate study conducted by the University of Arizona.

For example, with 37/37 match there is a 50% probability that the MRCA was no longer than 2 generations, and a 90% probability that the MRCA was within the last 5 generations.

Compare these with 25 and 12 -- with 25 markers, there is a 50% probability that the MRCA was within the last 3 generations, while with 12 markers, there is a 50% probability that the MRCA was within the last 7 generations.

For a chart showing the Probability for Most Recent Common Ancestor (MRCA), see: http://www.familytreedna.com/faq2.html

SO, in conclusion, if your test results fits within one of the above scenarios, it may be advantageous to upgrade to a 67 marker.

In time, there may be an increase in available markers to test so upgrading to a 67 marker may be only a step to the future and not the end.

©aulcino@hevanet.com, 1 Nov 2008


M. Richardson said...

Surely the better way to argue the case for more markers were if fewer markers weren't able to differentiate between the surname under research and other surnames. Even for the most common surnames (Smith, Walker, Brown etc.) it hasn't been necessary to go to 67 markers. The data at SMGF uses fewer markers with excellent resolution of groups.

I understand that additionally tested markers allow for additional chances to observe mutations and thus show sub-groups within a larger group, but is 67 the right number, or 670? Or could you have seen the same information at less than 67? What would you consider the best number and how would you quantify it?

In your own project, is there good evidence that 67 markers has resolved any further groups of significance? If so, at what cost? There was a time when genetic genealogists were told 12 markers was good enough. I believe by the same company. I guess I'm saying take caution in what you are being sold as it sounds like the message alters if you listen to the marketing dept vs. taking a hard look at data. There's a very good reason to question it as ultimately you are asking your own relatives to buy into it too.

Genealem said...

Thank you for your comments. I was not suggesting that everyone should upgrade to a 67 marker. I was only giving some reason why it could help. It surely isn't necessary to have 67 markers to know if one belongs to a particular surname.

Sixty-seven is the current maximum amount for Ydna in the genealogy area. Only if more markers are determined to be helpful in breaking people down into subgroups even further would it be necessary to increase the number of markers. I doubt that 670 on the Y-chromsome would be practical.

There is no "best number" for any one situation. Much of it depends upon the tester's goals and the findings within the project.

In one of my projects we have a large group who matches with some mutations. Some of them with perfect matches until they upgraded to a 67 marker. In particular, one person who couldn't determine the common ancestor to the larger group found he had a mutation in the markers between 38 and 67. Now when he finds someone with the surname who matches him, but has that unique marker, he will know there is a closer match than with the group. This can help focus the research to a more specific situation.

I also have a group who matched at a 12 marker, but was all over the place with a 37 marker upgrade. It was just a bit more than the average mutations for a 37 marker. They sworn their paper trails were solid. We tested more people and found the newer testers were bridging the gap. After upgrading to 67 markers we found a better percentage of markers matching and led us to resolve that this family mutated more than the average.

SO...yes, one needs to set their own goals for testing, work with their administrator to understand all this and whether any upgrade could be helpful or not.


Dave Cook said...

Emily - A little late to this conversation, but I discovered something tonight that makes me have more confidence in a very close 67 marker match my line has with another. My Cook line from KY has a 65/67 marker match with a Koch line from PA. One of my early Cooks went by "Dutch" and I could never figure out why. Then I found this tonight: "The Pennsylvania Dutch, are not Dutch, but are of German and German speaking heritage, They are the descendants of the early German speaking settlers of the inland counties of Pennsylvania who arrived in Pennsylvania prior to the Revolutionary War."

How much confidence can I have in a 67 marker match with 2 mutations?

Genealem said...


You can have a lot of confidence in the 65/67 match. That's very good. AND...with your line being German, it is possible that Koch and Cook really have the same roots. Often names were altered. To know the really pronouciation of the German Koch could help. I have German line with the ancester being Thones Kunders. Surprisingly, I have learned that his being called Dennis Cunard isn't far from the German pronouciation. I was shocked, but this comes from a person who knows German and German research.

Deborah Richards said...

Hello, I have browsed most of your posts. This post is probably where I got the most useful information for my research. Thanks for posting, maybe we can see more on this. Are you aware of any other websites on this subject.aabb dna testing for uscis