Wednesday, May 4, 2011

Comparing 111 Markers in Y-chromosome DNA Research


I have had my 111 marker Y-chromosome DNA results back from the lab for a couple of weeks. That was exciting but it was essentially meaningless. DNA test results for genealogical purposes only take on significance when there are others in the database with whom meaningful comparisons can be made. Last night I noticed that my first match was with Herb McDaniel. Herb and I have previously had matches at lower resolutions. We matched on 35 of 37 markers and 64 of 67 markers. Our new results show that we match on 102 of 111 markers.
What does this mean? Are we now shown to be more or less likely to have a common male ancestor within genealogical time? Genealogical time is defined as the era in which most individuals have had surnames.
Both Herb and I have solid paper trails of our respective paternal lines that go back 8 generations. Also both of us have been able to triangulate our first 67 markers of our Y-chromosome DNA enough to be reasonably confident that each of us exactly matches those markers of our 5th or 6th great-grandfathers. This knowledge allows us to make a slight adjustment in the information provided by FTDNATiP™ which is employed by Family Tree DNA to create probabilities of a shared common ancestor within the last so many generations. In our case we believe that Herb's paternal McDaniel ancestor and my paternal Dowell ancestor were exactly as many markers apart eight generations ago as Herb and I are today. Well we believed this prior to getting the results back on markers 68 to 111. Only time will tell if we can further refine our thinking based on these latest results.
Below are four different columns probabilities that Herb and I share a common male ancestor. Each of them are listed in this table at 4 generation intervals. However, they could easily be displayed for every generation. Again, based on a combination of paper and DNA research, we do not believe we are related within the last 8 generations. In general the addition of markers 68 to 111 appear to strengthen the probabilities that we share a common male ancestor over all the intervals but particularly after 10 to 12 generations.
Generations To Common Ancestor
67 Markers
(64/67 match)
67 Markers
Adjusted
111 Markers
(102/111 match)
111 Markers
Adjusted
8
8.34%
3.79%
25.60%
10.85%
12
33.64%
30.35%
65.55%
58.72%
16
63.47%
61.65%
89.39%
87.29%
20
83.99%
83.20%
97.56%
97.07%
24
94.12%
93.83%
99.54%
99.45%
28
98.12%
98.02%
99.93%
99.91%

* "The FTDNATiP™ results are based on the mutation rate study presented during the 1st International Conference on Genetic Genealogy, on Oct. 30, 2004. The above probabilities take into consideration the mutation rates for each individual marker being compared."

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