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Some yDNA Results and Conclusions

 

 

        We now have enough yDNA results from the Henry Woody line to reach some interesting conclusions. The following discussion is somewhat complicated and I have tried to condense the ideas as much as possible. In truth, I may have over simplified the concepts and explanations; however, the basic conclusions seem valid to me. This discussion was revised on 29 September 2008 to reflect the number of mutations attributable to mismatches of the DYS 464 marker. This rather unintuitive calculation is explained  here. This revision has not altered the conclusions.

         It is well known that DNA genetic markers mutate over time. This characteristic is called polymorphism. The number of mutations per hundreds of generations is called the mutation rate. In the early days of genetic studies (c. 2001), an average mutation rate of .002 or .2% was thought to be accurate. However, in 2004, FamilyTreeDNA (FTDNA) indicated that the average mutation rate for the general population was .004 or .4%.  Note that this is the
average mutation rate for all markers in the general population. It is also well known that the mutation rates for the individual genetic markers are not the same.

        To estimate how long ago a connection between two individuals occurred, the concept of Generic Distance (GD) was introduced.  Very basically, the GD tool uses the number of marker differences (mutations) between individuals to estimate the probability of the Time to the Most Recent Common Ancestor (TMRCA) in years or generations. FTDNA has widely publicized that it uses different mutation rates for each genetic marker when computing GD and TMRCA. Although FTDNA does not publish the specific mutation rates, it appears that they may be using a rate of .007 for some markers. However, most tools that compute TMRCA use the
average mutation rates for the general population, even if different average rates are used for each marker. This includes the FTDNATIP and GD tools at FTDNA. Obviously, since each marker has an average mutation rate for the general population, there must be rates that are higher and lower than the average.  In fact, some surname mutation rates are much higher than average and some hardly mutate at all. Over the years, it has become apparent that the markers associated with a very few surnames mutate at a much
higher rates than those for the average population.  Although this phenomenon is quite rare, it appears that the Henry Woody line falls into this category.

        Using the 37 marker data that we have accumulated for five descendants of Henry Woody, we have calculated an average mutation rate of .0079. This translates to an Average Marker Duration (AMD) of 3.4 generations. For 37 markers, this means that we can expect to see, on average, a marker mutation every 3.4 generations. By way of contrast, a .002 rate would produce a 13.5 generation AMD and a mutation rate of .004 would produce a 6.67 AMD.

        If you look at the yDNA project results of most surnames you will see line after line of exactly identical or very similar results for many individuals. This is to be expected since the average mutation rate of most surname markers is .004. This rate produces a mutation, on average, every 6/7 generations and 6/7 generations is the extent of many lineages.  In contrast, the 37 marker results for the five descendants of Henry Woody do not contain a single exact match. This is because we can expect to see, on average, a mutation every 3.4 generations. Since most of our Henry Woody lineages are 6 generations, we can expect to see at about two mutations for each individual during this period.

        There is one online tool that calculates TMRCA and also allows the selection of an average mutation rate. To use this tool, go to Dean McGee’s
Y-Utility: Y-DNA Comparison Utility, FTDNA Mode
. Using an average mutation rate of .0079, we have used this tool to analyze the yDNA markers of the five descendants of Henry Woody.  The table below shows the results of using the tool. These results are in close agreement with our paper trails for the five individuals.

 

Time to Most Recent Common Ancestor (Generations)
ID m
o
d
a
l
 
W
-
8

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
9

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
1

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
1
3

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
1
4

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
modal 37 3 5 5 5 5
W-8 Henry Woody R1b1b2 3 37 3 7 7 7
W-9 Henry Woody R1b1b2 5 3 37 8 8 8
W-1 Henry Woody R1b1b2 5 7 8 37 8 5
W-13 Henry Woody R1b1b2 5 7 8 8 37 8
W-14 Henry Woody R1b1b2 5 7 8 5 8 37
0-9 Generations 10-19 Generations 20-29 Generations 30-39 Generations
- Infinite allele mutation model is used
- Average mutation rate: 0.0079
- Values on the diagonal indicate number of markers tested
- Probability is 50% that the TMRCA is no longer than indicated
 
 

 

        The tool confirms our paper trails, but we would really like to use the tool to estimate how closely individuals with shorter paper trails are connected to our five descendants of Henry Woody. The chart below shows the results of adding the markers of Austin Woody to those of the five descendants of Henry Woody and running the tool using the same .0079 average mutation rate. As can be seen, Austin and Henry had a common ancestor in their near past: Perhaps that ancestor was Henry’s grandfather.

 

Time to Most Recent Common Ancestor (Generations)
ID m
o
d
a
l
 
W
-
8

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
9

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
1

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
1
3

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
1
4

H
e
n
r
y

W
o
o
d
y

R
1
b
1
b
2
 
W
-
2

A
u
s
t
i
n

W
o
o
d
y

R
1
b
1
b
2
 
modal 37 3 5 5 5 5 8
W-8 Henry Woody R1b1b2 3 37 3 7 7 7 7
W-9 Henry Woody R1b1b2 5 3 37 8 8 8 8
W-1 Henry Woody R1b1b2 5 7 8 37 8 5 8
W-13 Henry Woody R1b1b2 5 7 8 8 37 8 12
W-14 Henry Woody R1b1b2 5 7 8 5 8 37 10
W-2 Austin Woody R1b1b2 8 7 8 8 12 10 37
0-9 Generations 10-19 Generations 20-29 Generations 30-39 Generations
- Infinite allele mutation model is used
- Average mutation rate: 0.0079
- Values on the diagonal indicate number of markers tested
- Probability is 50% that the TMRCA is no longer than indicated
 
 

        The pioneering research on calculating the actual mutation rates of DNA markers associated with surname groups was done by Charles F. Kerchner. We have borrowed heavily from Charles’ work and used his method of calculations to arrive at the mutation rates in the above discussion. Those wishing to explore this topic in more detail should start with Kerchner's DNA Testing & Genetic Genealogy Info and Resources Page. We expect these rates to change somewhat as we accumulate more data, but we do not expect the conclusions to change.


Conclusions


The yDNA markers of the descendants of Henry Woody have a very high average mutation rate.
This is a rare phenomenon that seems to be associated with certain surnames.

The DNA testing companies have not provided adequate tools to do comparative analysis of the yDNA markers of individuals in surname groups with very high average mutation rates.  This is because the number of individuals and surnames with these high rates is very small. The GD and TMRCA tools that they provide are based on the average mutation rates of the general population and satisfy the needs of the vast majority of surname lineages. These traditional TMRCA and GD tools have very little value when used to analyze the DNA results of descendants of Henry Woody.

There is a TMRCA tool available that allows the selection of an average mutation rate.

Very fast mutating markers have the potential of aiding those Woody descendants with short paper trails.
 

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Revised Jan 14, 2012