1. With several levels of Y-DNA test being offered, how does one know which is the right one to choose? If I submit a sample to you for testing and you find that I match exactly with another person, how many generations ago did we have a common ancestor?
Is the 37-marker test not enough? Why the need for a 67-marker test?
Our motivation to offer a 67-marker test was two fold:
1. Family Tree DNA wanted to ensure our customers that by testing with us they could obtain the highest resolution Y-DNA test in the world (like FTDNA clients may also obtain the highest resolution test on their mtDNA by taking our Full Genomic Scan, which looks at the entire mitochondria molecule).
2. Several groups of families have still not been able to completely determine the relatedness of group members with our flagship 37 marker test. Therefore we see two main advantages of testing 67 markers over testing 37:
-
Y-DNA67 can further refine our estimate of how closely related two individuals are,
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By using additional markers groups of related participants have a better chance of finding mutations which identify sub-branches in the family.
However, not all participants or projects need to test 67 markers in order to achieve their objectives.
Some projects will be able to achieve their goals with a 12, 25 or 37 marker test. Only if you are in a project and part of a subgroup of that project where you match, exactly or nearly exactly, to several others will you gain by upgrading to additional marker.
Our motto could be: test only what you need, upgrade only when necessary.
Here are the times back to the MRCA when ALL the markers match. Those numbers are based in the latest results of the mutation rate study conducted by the University of Arizona. For example, with 37/37 (all 37 markers 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.
Table 1. Probability for Most Recent Common Ancestor (MRCA)
Number of
matching markers |
50% probability that the MRCA was no longer than this number of generations
|
90% probability that the MRCA was no longer than this number of generations
|
95% probability that the MRCA was no longer than this number of generations
|
10 of 10 |
16.5 |
56 |
72 |
11 of 12 |
17 |
39 |
47 |
12 of 12 |
7 |
23 |
29 |
23 of 25 |
11 |
23 |
27 |
24 of 25 |
7 |
16 |
20 |
25 of 25 |
3 |
10 |
13 |
35 of 37 |
6 |
12 |
14 |
36 of 37 |
4 |
8 |
10 |
37 of 37 |
2 to 3 |
5 |
7 |
65 of 67 |
6 |
12 |
14 |
66 of 67 |
4 |
8 |
9 |
67 of 67 |
2 |
4 |
6 |
FamilyTreeDNA's 37 and 67 marker tests point to a much lower number of generations to the most recent common ancestor than other commercially available tests. We use exacting statistics appropriate for the non-independent transfer of genetic material on the Y Chromosome.
Table 2. Examples of previously tested individuals.
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