This project is not part of Ancestry.com DNA sales. This project uses http://www.familytreedna.com   

Web space provided by rootsweb.com, sponsored by ancestry.com.

Please read notice in the bottom bar.

Advertisements at the top and bottom of the pages are not part of this project, 

visiting the links helps pay for the website space 

~~~~~~~~~~~~

Time to the Most Common Recent Ancestor and Mutation Rates

By Roberta Estes (copyright 2008)[1]

One of the most frequently asked questions is how to effectively determine and use the Time to the Most Common Recent Ancestor (MCRA) and the TIP tool provided by Family Tree DNA.

You can access your TIP reports by clicking on the “My Matches” line on your Family Tree DNA personal page.  Those with a similar surname will have a little red box that looks like a pedigree chart to the right.  Click on that box and it will run the Tip report for you and the individual whose red box you clicked. 

The results will be presented to you in percent of probability and will look like this:

The two men in question above do in fact share a common ancestor 8 generations ago.

This tool was created by Family Tree DNA to give individuals a broad brush idea of when they might related to another participant, or conversely, if they are not related.  Clearly, this is not an exact science, and furthermore, it relies heavily not only on your own results, but on statistical calculations of probability.  While these calculations are very useful in population genetics, the closer one moves in time to the present, the less useful these calculations become.  Why?  Let’s take a look.

Let’s talk first about using mutations and mutation rates to determine the length of time that two individuals might converge in a common ancestor.

Mutation rates on the average and for various markers vary WIDELY, and I do mean widely.  In one case, I know of a particular family whose mutation rates in 19 generations are 250 times greater than the average mutation rates.  I know of another family whose rates are significantly lower, nearly zero, in about the same number of generations.  Obviously, both of these are the outliers, but remember that average mutation rates are made up of just these things.....everyone's rate is put into the pot and they are all added together and then divided by the total number.  So that rate may or may not be relevant to you or your ancestors.  I strongly discourage people from trying to figure out or correlate a genealogical connection between two individuals by using these rates or the number of generations given.  It's just not a science refined enough for that yet.

The good news is that when you run the Tip report for 37 markers or higher, Family Tree allows you to modify the information using genealogical information, if you have it at your disposal, which will make the numbers more meaningful, but still nothing approaching what we would like to see.

So the next logical question is why some of your ancestral families (typically within surname projects) have no mutations and others have several.  Let's look at how averages are constructed.  If any given marker is on the average (remember what an average was from above) going to mutate once in every 15 generations, that means that some will not mutate at all, some will mutate more than once, but on the average you will see one mutation in 15 generations for that particular marker.  This 15 generation number is just an example, as each marker has its own mutation rate.  So a mutation could happen in the first generation, or the second, or the third, etc.  If on the average you have 1 mutation every 15 generations, you don't know what "click the clock is on", you only when you started looking.  This means that the mutation could have happened is the generation just before you began looking (i.e. your next oldest ancestor whom you have yet to find) and you won't see another one for 14 generations, or it could mean that you're "due" and the mutation happens immediately.  It can also mean that you're NOT due, but you can still have a mutation anytime. 

So, we have several factors at play here and whether or not we can measure, understand or change these factors.

First, the calculated average mutation rate for all markers. This number can be calculated and is often used, but bears little relevance to individual marker or family mutation rates.

Second, the individual mutation rate for any particular marker. This can be calculated and is used by Family Tree DNA. However, several unknowns remain, specifically, whether or not a marker is more likely to mutate in one direction or the other, or whether markers on the higher or lower end of the spectrum are more likely to mutate that markers in the middle of their spectrum.

Third, the personal mutation rate of your own family's DNA.  This can be calculated but you’ll need several individuals with solid genealogy connecting to a proven ancestor to be able to do this.  Family Tree DNA calculations don’t include this information as they have no information with which to calculate it.

Fourth, the personal mutation rate of any particular marker in your family. Same commentary as three above.

Fifth, the "click of the clock".  This remains unknown. 

Sixth, the mutation rate of the haplogroup.  This variable is undocumented for the most part, but the fact that there is a variance is accepted in scientific circles.  How much bearing this has on the rate of the click of the clock is at this time unknown, and the degree of effect that would come to bear from variations in the haplogroup mutation rate versus the individual family mutation rate could be very difficult to determine.

Seventh, generational length, which you could modify somewhat based on any knowledge about your ancestors and family patterns if known.  For example, in some cultures, generation length average was much shorter as women began producing as soon as they were physically able.  In other cultures and times, women didn’t marry until they were between 21 and 25, which greatly affects the number of children they can expect to produce within their lifetime, and the average generational length.  This variable can indeed be tweaked within the Family Tree DNA tip calculator when evaluating over 37 markers.

Eighth, where the mutations happen to fall in the three panels.  For an example of this, see the final example below.

The best you can do with all of this is to use the tools provided by Family Tree DNA in their TIP program, but understand just how general these tools are (by the necessity of the above factors) and only use them as a very general reference.  In particular, do not run the tip calculator and begin counting up the pedigree chart to the 10^th generation and decide that surely this must be the common ancestor.  You may be right, but chances are, you’ll be wrong.  The TIP calculator and common ancestors are much more reliable when working with very large timeframes over which to smooth out the effects of the outliers.  For example, in the Estes example shown initially, the calculator is correct that the two men do share a common ancestor within 24 generations, and within 20, 16, 12 and 8.  However, that calculation is based on 2 mutations in 37.  If those 2 mutations fell within the first 25 markers, their report would look like this if run against only 25 markers instead of 37:

If the mutations for these two gentlemen fell only in the third panel, then they would match at 100% if they had only tested 25 markers, and then their report would look like this:

Remember that this example is using the same number of mutations but placing them in different panels and running the tip against either the 25 or 37 panel models. 

The moral of this story is that we should use all of the tools available to us, with our eyes wide open, and always, always evaluate the scientific data in light of the genealogical information available. However, like most everything else in life, there is an exception to the rule.

If the DNA says you’re not related, then you’re not related.  I have intentionally selected two men who I know are not related to demonstrate this phenomenon. 

DNA can disprove genealogy, but genealogy cannot disprove DNA.  However, these statistical tools are not infallible. 

Another handy feature provided by Family Tree DNA is a chart that gives rules of thumb for matches and mismatches. Generally, I would agree with this, but again, averages are compiled by including all of the data, including outliers, and this is not gospel, it is a statistical guideline.  Looking at the following chart provided at http://www.familytreedna.com/gdrules_12.html, keeping in mind that while we do call 3 mutations in 12 generally “unrelated”, if these same 3 mutations were the only ones out of 37, we’d be calling the two people “related”. It is possible, if improbable, that someone could have 3 mutations in the first panel and match on the rest.  The only way to know is to perform further testing. 

For more detailed information about the TIP calculator, refer to the FAQ page at http://www.familytreedna.com/faqtip.html.

Under what circumstances can we best utilize these tools?  I use these tools most often to determine whether people with differing surnames are related in a genealogical timeframe, especially if I find them co-located.  Again, TIP is most accurate the further back in history you can reach.  It is particularly useful in answering questions like are the McMahon family and the Estes family really descended from a common ancestor and if so, in what timeframe might we reasonably expect to find that common ancestor.  I also use TIP as a sanity check when the genealogy is questionable. 

TIP is useful if we don’t expect it to perform more than it can, don’t use it to mis-set our expectations and or to “confirm” things like “two men share an ancestor within the last 8 generations”. TIP can’t do that, and this type of misconception and over-interpretation is all too common with excited first time participants who have just received their results.  Using this tool correctly and understanding the results can indeed help us move our genealogy project forward by accurately utilizing both genetics and statistics. 

Contact Information: 

Electronic mail

General Information/Project Membership: [email protected] 
Webmistess: [email protected]

Notice

The Lost Colony Research Group is in NO WAY affiliated with The Lost Colony Center for Science and Research.  The Lost Colony Y-DNA and MT-DNA projects at Family Tree DNA are NOT IN ANY WAY  affiliated with The Lost Colony Center for Science and Research,
regardless of what their links imply.

"Please notify us of any claims to the contrary."

~~~~~~~~~~~~~~~

There is no fee to join our group and no donation of monies or objects are needed to participate in "The Lost Colony Research Group".

~~~~~~~~~~~~~~~

As with any DNA project, individuals pay for their own DNA testing, but the
group itself  - is strictly volunteer and free to join, upon approval of membership.

~~~~~~~~~~~~~~~

Neither Rootsweb.com, myself, nor the Lost Colony Research Group together or individually are  responsible for the personal content submitted by any individual to this website.

Send mail to [email protected] with questions or comments about this web site.
Copyright © 2008 Last modified: October 10, 2010