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Here are the questions and answers you may have about the FTDNATiP™ - Family
Tree DNA Time Predictor.
- What is so special about FTDNATiP™?
- Bob, John and I have the same Genetic Distance. However when compared between
each other we have different probabilities for sharing a common ancestor
within, for example, 8 generations. Why?
- When comparing two individuals the DNA test shows them to be closely related.
However, one has my surname, and the other does not. Does the match with the
similar surname mean we are more closely related?
- I have genealogical information. How does FTDNATiP™ use it?
- Would more markers enhance the calculations?
- When will FTDNA publish the mutation values for each maker?
- How often are the mutation rate estimates updated?
- Why does the Report page sometimes show a difference between the Genetic
Distance and the number of mismatches?
- A group of us have been working to confirm the genetic signature of a specific
line. I used the FTDNA TiP calculator to calculate the probable amount of time
to their common ancestor. Next, I increased the number of generations to 7. As
expected, the results changed. However, our question to you..... Why did the
probability become less when we eliminated the possibility of a common ancestor
within the past 7 generations? It seems that it should increase?
- When does the ability to enter genealogical information appear? I am trying out
the new FTDNATiP, and I noticed that sometimes it provides the ability to enter
the number of generations, and sometimes it doesn't. I haven't figured out the
pattern yet - can you clue me in?
- Who is 1 generation ago?
- How do I find out the time to the MRCA in years?
1. What is so special about FTDNATiP™?
FTDNATiP™ is the world's first program that incorporates specific mutation rates
that have been proven to differ across markers, which greatly increases the
power and precision of estimates of Time to the Most Recent Common Ancestor
(TMRCA). Coupling this program with the results of a recent mutation rate study
conducted by the University of Arizona, and presented by Family Tree DNA at the
1st International Conference on Genetic Genealogy on Oct. 30, 2004, has
resulted in an extremely powerful new tool for genealogists.
The U of A mutation rate study generated values significantly higher than those
typically reported in the literature, and incorporation of these marker
specific higher rates into FTDNATiP™, results in an analysis when using 37
markers that is as powerful as a 56 marker test using the method of analysis
currently applied by other genetic genealogical companies.
These results arose from collaboration between FTDNA, the Arizona Research Lab,
which is one of the world leading laboratories for Y Chromosome research (lead
by Dr. Michael Hammer), and one of the world’s leading statistical geneticists,
Dr. Bruce Walsh.
The FTDNATiP™ calculations take into account the specific mutation rates of the
first 37 markers, and until mutation rates are determined through study for the
final 22 markers the FTDNATiP™ calculator will use an average mutation rate for
that last panel.
2. Bob, John and I have the same Genetic Distance. However when
compared between each other we have different probabilities for sharing a
common ancestor within, for example, 8 generations. Why?
Genetic Distance by itself is a simplified measure of the total number of
mutational differences between two individuals. FTDNATiP™, however, is unique
in the fact that it incorporates the specific mutation rate for each marker.
Therefore, while you and John may differ on DYS#394, if you and Bob differ on
DYS#439, the results will be different because those markers each have distinct
mutation rates. FTDNATiP™ takes this into account while a simple Genetic
Distance calculation does not.
3. When comparing two individuals the DNA test shows them to be
closely related. However, one has my surname, and the other does not. Does the
match with the similar surname mean we are more closely related?
Perhaps. There are several reasons why related individuals may not share the
same surname (undocumented adoption, false paternity). While shared similar
surnames coupled with a very high percentage of Y marker matches indicates a
very high probability of recent common ancestry, a high match with a
non-matching surname can also provide evidence of recent common ancestry. If
the comparison is made with our 12 marker test, it may make sense to upgrade to
a 37 or 67 marker test to increase the precision or further exclude the
probability of a recent common ancestor.
4. I have genealogical information. How does FTDNATiP™ use it?
FTDNATiP™ is unique in allowing you to incorporate your assumptions (based
either on a solid genealogical paper trail or an informed guess on your part)
on the earliest possible generation of a common ancestor into the DNA match
calculations. For example, if you can exclude any chance of a common relative
between you and another individual within (say) the past 3 generations, you
enter this information, and FTDNATiP™ computes the time to common ancestry
based on both the marker pattern and your assumption that the common ancestor
must be at least 4 generations back.
5. Would more markers enhance the calculations?
Yes, but with greatly diminishing returns. The current 37 and 67 marker tests
are extremely powerful because they contain a number of markers chosen for
their very high mutations rates. By incorporating the known mutation rates of
all the 37 markers, the resulting power of the FTDNATiP™ estimator is akin to a
56-marker test that makes the assumption that all mutation rates are the same
based on a mutation rate of 0.004, or 110-marker test based on a mutation rate
of 0.002. FTDNATiP™ is unique in incorporating marker-specific differences,
generating considerably improved power relative to any other analysis.
6. When will FTDNA publish the mutation values for each maker?
The results will be posted by FTDNA when the final University of Arizona study
is published in the literature.
7. How often are the mutation rate estimates updated?
The current estimates are based on over 130,000 meioses (transmission events)
analyzed in the Hammer laboratory. As additional known genealogies are added to
the databases, updated estimates of the marker mutation rates will be generated
and incorporated into FTDNATiP™. The date of the current mutation rate estimate
set is given at the bottom of the FTDNATiP™ printout, allowing you to see if
the estimates have been updated since you last ran your results.
8. Why does the Report page sometimes show a difference between
the Genetic Distance and the number of mismatches?
Genetic Distance is a measurement that does not take into consideration
mismatches that are a result of single events. FTDNATiP™ uses the infinite
allele model as opposed to the stepwise model, and that's why, for example, a
two step mutation in a single marker is considered one mismatch even though it
will read as a Genetic Distance of 2.
9. A group of us have been working to confirm the genetic
signature of a specific line. I used the FTDNA TiP calculator to calculate the
probable amount of time to their common ancestor. Next, I increased the number
of generations to 7. As expected, the results changed. However, our question to
you..... Why did the probability become less when we eliminated the possibility
of a common ancestor within the past 7 generations? It seems that it should
increase?
Remember, we are talking cumulative probabilities. That's the key to
understanding something that initially seems counter intuitive.
Let's use an example for a specific situation of one mismatch in 37 markers.
Before inputting your information, the chance of having a common ancestor in
the first 4 generations is 59.03% and chances for having a common ancestor in
the next 8 generations (between generations 4 and 12) is 97.48 minus 59.03, or
38.45% . Now, with the new information that there were no common ancestors in
the last 7 generations, the chance of having a common ancestor between 7
generations ago and 11 generations ago is 75.55%. In other words, this new
information not only increased the percentage, but also increased the focusing
time from 4-8 generations to 7-11 generations.
10. When does the ability to enter genealogical information
appear? I am trying out the new FTDNATiP, and I noticed that sometimes it
provides the ability to enter the number of generations, and sometimes it
doesn't. I haven't figured out the pattern yet - can you clue me in?
The box to enter the number of generations appears only when you are not
comparing a perfect match: i.e., when there are mutations between the 2
individuals. The reason why this option is not offered in a situation of
perfect match is because statistically it doesn't matter when it's a perfect
match - you will get the same percentages moved back by that number of
generations.
11. Who is 1 generation ago?
We start counting generations with the parent generation. Therefore, the father
of the person tested would be 1 generation ago, the paternal grandfather 2
generations ago, etc.
12. How do I find out the time to the MRCA in years?
You can convert the generations to years by multiplying the number of
generations by an average number of years between generations. In general, you
can use an average of 25 years per generation, although the average can vary
from family to family.
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