Using 12 marker STRs for Group Placement ?

Anyone wishing more information can email me at stancourtney@gmail.com



In the early 2000's genetic testing became available for genealogists. For most people their primary concern is to be placed within their correct group and to match other Courtneys.

12 marker STR testing was introduced by FamilyTreeDNA in July of 2000. The major problem with the group placement of people using only 12 markers is that the amount of matches can be quite large. I have seen one member who matches over 12,000 other men. 12 marker testing show other men who may be thousands of years apart for common ancestors, obviously there is a problem of 12 marker not be refined enough.

37 marker STR testing was introduced by FamilyTreeDNA in January of 2004. At 37 marker typically the number of matches drops off dramatically. The member who had over 12,000 matches at 12 marker has now dropped to 140 matches.

67 marker STR testing was introduced by FamilyTreeDNA in June 2006. Today, 67 markers is considered the "gold standard" for STR testing. The member who had over 12,000 matches at 12 marker, dropped to 142 matches at 37 markers, and now at 67 marker has dropped further to 10 matches, all Courtneys plus a couple of NPE's.

I like to use the crude analogy of using a fishing net to catch large Chinook salmon. If I use a very fine mesh (12 marker) not only do I catch Chinook salmon but unhappily I also catch many species of unrelated fish. As I move up to a larger size mesh net (67 marker) the smaller fish fall through and eventually all I have left is the largest salmon, hopefully all Chinook salmon.

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STR matching does not fit this analogy exactly as in some cases 37 or 67 marker may show matches not seen at 12 markers. Many researchers turn off the 12 marker notification meaning they will not show up in matches for the lowest levels.

Kit # N134063 is a member of Group 23a a descendant of Robert Courtney of Onslow d 1751.

At 12 markers kit # N134063 matches men in the following groups, obviously there is a problem relying on 12 markers alone for placement.

Group 20, Group 22, Group 23a, Group 26, Group 33, Group 34.

My recommendation is to at least test to 37 markers when you test the first time. FamilyTreeDNA has discussed eliminating 12 marker testing altogether and with 3 or 4 major sales every year the upgrade is available at a reduced price.