YDNA. Snoddy

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Snoddy Tapestry
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Data
Notebooks
Analysis
Graphics
Bibliography
Index
……………………..The Tapestry
Families Old Chester OldAugusta Germanna
New River SWVP Cumberland Carolina Cradle
The Smokies Old Kentucky

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Documentation

A Snoddy YDNA project using FTDNA provides YDNA data for a limited number of test subjects.

Data

The following table summarizes the results of the Snoddy YDNA project as of 27 May 2010. Results for 12 markers are publically available. It is not known if additional markers have also been tested.

Signature/
Test Subject
13231411 1115 12 12 11 14 13 30Earliest ancestor identified by participant
A13231411 1115 12 12 11 15 13 31Person:John Snoddy (4)(ca 1720 - 1784)
B13231411 1115 12 12 11 14 13 30Samuel Snoddy (ca 1800 - ca 1855)
C13231411 1115 12 12 11 14 13 30 Andrew Snoddy (1826 - ?)
D13231411 1115 12 12 11 14 13 30 Samuel Snoddy (1727 - 1806)
E13231411 1115 12 12 12 14 13 30 Person:John Snoddy (4)(ca 1720 - 1784)
F13231411 1115 12 12 11 14 13 30 Andrew Snoddy (1843 - 1909)

Discussion

Test results displayed for the Snoddy YDNA Project include data for 12 markers. It is not known if additional markers have been tested, and are not displayed. The project may be limiting itself to 12 markers in the belief that, given the rarity of the surname, more in-depth testing is not needed. Perhaps compensating for this is the projects data-rich family history website. See Data:Snoddy YDNA Summary Table

Given the fact that only 12 markers are publicly available as results for the six test subjects, only a limited analysis is possible. One test subject (E) differs from the Modal Signature by one point mutations, and another (A) by two point mutations. Tests subjects A and E differ from each other by three point mutations.

The following provides interpretative data for a 1, 2, and 3-off test results when 12 markers are tested:

For a 12 marker test:

Markers
tested
Probability *MismatchesThis table shows the relationship between the number of markers tested, the number of mismatches observed compared to the Modal YDNA Signature, and the probability that the MRCA lies a certain number of generations back. For example, if persons A and B take the YDNA test for 12 markers, and show an exact match on all 12 markers, there would be a 50% chance that their common ancestor lay within the last seven generations back, and a 90% chance that he lay within the lasts 17 generations.
012
12 50% 7 17 -
90%2339 -
95% 29 47 -
25 50% P3 7 11
90% 10 16 23
95% 1320 27
37 50% 2-34 6An exact match in a 37 marker test indicates that the MRCA lies within the last 2 to 3 generattions about 50% of the time, and within the last 6 generations 95% of the time.
90% 5 8 12
95% 7 10 14
67 50% 2 4 6Increaseing the number of markers to 67 only marginally improves the the information returned from a YDNA test.
90% 4 812
95% 6 9 14

* X% probability that the MRCA was no further back than this number of generations, given the number of mismatches shown
Data from FTDNA 27 May 2010

Most of the test results in the Snoddy yDNA tests show an exact match on a 12 marker test. this suggests that 50% of the time the common ancestor of the test subjects would lie within the last 7 generations. If one chose, one could approximately convert the above data concerning "generation to MRCA" to "years to MRCA" by multiplying by an estimate of the time between generations. A value of between 20 and 25 years is often used for this purpose. If you assume a 22 year generation time, than at 50% probablity the Common ancestor would lie about 150 years prior to the birth of the test subjects. Assuming the test subjects were all about 50 years of age, then we get a MRCA sometime within the last 200 years (e.g., born around 1760). On the other hand, the MCRA would have occurred earlier than 1760 about half the time as well. As a result, its difficult to evaluate the meaning of a perfect 12/12 test result.

ON the otherhand, test subject A mismatched with most of the other test subjects by 2 marker3 (a 10/12 match). This tells us that the MRCA for test subject A, and most of the rest of the test subjects lay more than 17 generations in the past at a 50% probability, and at 47 generations at a 95% probability. Converting this into time to the MRCA, we get an estimate that at 50% probability the MRCA lay more than 400 years, and at 95% probability more than the last 1100 years or so. The significance of this is that it is very unlikely that test subject A is closely related to any of the other test subjects, at least in a genealogically meaningful timeframe.

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