Questions and Answers that have come up.
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St * r * * v * nt GENETIC Project
FAQ
Below are questions and answers that have come up during the life of this project. If your question is not answered here, please contact me at nospamjssturdevant@bresnan.net. Copy the address into the address line of your email program, then remove the nospam.
Question
How does the number of markers relate to proof of ancestry?
Answer
We can see how it works with a graph. Family Tree DNA has provided one here:
If you open a new window in your browser, File New Window, click the above link, and look at the bottom chart:
Probability of Common Ancestor is on the left,
Number of Generations to that Common Ancestor is on the bottom,
What you see is:
- The brown/red line is the 12 marker test. It takes 40 generations to get to a 80% probability of a common ancestor. For all intents and purposes it never gets to a 95% probability.
- The green line is a 25 marker test. It takes half as long to get to the 80% probability, 20 generations, and rises to 95% probability within 30 generations.
- The blue line is the 37 marker test. It gets to 80% probability within 10 generations.
It all depends on what probability are you willing to accept. If it is more than 50% probable (5 generations on a 37 marker test) that you have a common ancestor; is that good enough for you?
Once we get more results in, we will be able to test the probabilities.
Question
Two members from the group had "Some questions:
the 43 marker issue-what exactly does that mean and what is supposed to be measured
and what do we do about it? Do WE choose the markers of the 43?
Answer
I have tried to put links on the web site that explain the ins and outs of DNA testing. I realize it is heavy going, and I certainly do not understand all of it yet. I did not want to be the only voice on this subject, and I have tried not to make any predictions on what our testing will show, preferring to let everybody interested inform themselves on the ins and outs. Then when we have the data we could try to figure what it all means. But some generalities that I gleaned:
In short, for the male y-chromosome
the more markers - the more possibilities of differentiation,
the more possibilities of differentiation - the greater the possibility of
determining precise ancestry,
because
if you have the same differentiation as someone else you are related
through a common male ancestor (same surname).
When we are talking about markers we are talking about points on the y-chromosome of the male. So we would be looking at 43 points on the y-chromosome to see how they compare with the same 43 points on another person's y-chromosome.
This comparison is done by counting the number of repeats of a sequence of letters. If the number of repeats at each marker is the same for two people then they have the same common ancestor (obviously a male). The more markers that are identical, the shorter the time to that common ancestor. An exact match of 43 markers shortens that time to 4 generations. (Your second great grandfather) The test does not say exactly who this common ancestor is though. The common ancestor has to be determined through genealogy.
Example:
Given Ray's (Sturtivant) thesis that all spellings of our surname world
wide come from one surviving branch of the surname in Nottinghamshire,
i.e. all males with any variant of our surname are all descendants of
William Sturtivant of Norwell Woodhouse in Nottinghamshire through his two
grandsons - John and Francis.
If we tested all those males with a 12 marker test, I would expect all those males to match on all 12 markers of a 12 marker test. This means we all had a common ancestor 14 generations ago. This time period would take us back to England, before the emigration, not quite to William of Norwell, but perhaps to John and Francis. (assuming that my William of Norwalk is 10 generations ago) If some individuals only match on 10 or 11 of those 12 markers, then the common ancestor is further back, perhaps William of Norwell.
If we tested all those males with a 26 marker test, differences should be showing up.Those who match all 26, have a common ancestor about 7 generations ago, about the time of John Sturdevant III and Mary Sanford in my line (1750). So if I match 26 markers with someone else, then that someone else is also a descendant of John Sturdevant III who married Mary Sanford and died in Shaftsbury Vt. It does NOT say if that person is a descendant of John IV, Samuel, Stephen, or James. (the 4 sons mentioned in John III's will). But it would certainly point a direction for research.
If two individuals match on 43 markers then the common ancestor is 4 generations ago. If I match all 43 markers with someone else, that person is also a direct male descendent of my second great grandfather, John Sanford Sturdevant of 1850 Bridgewater, Litchfield, Connecticut.
The number of markers can refine the detail.
Another way to look at it,
All male surnames of whatever variant would have 12 markers match.
All male descendants of William of Connecticut would have 26 markers match,
All male Descendants of Samuel of Massachusetts would match 26 markers,
all
male Descendants of John of Virginia would match 26 markers,
but 12 of
those markers should be common to everybody
The markers are not chosen by us, only the number of markers - through the price we pay.
All companies test the same 12 markers on a 12 marker test, and the same 26 markers on a 26 marker test. However they have differences in which markers are tested between the 37 and 43 marker tests. I do not have any idea whether one marker is better than the other. You can find lists of the markers tested by DNA Heritage and Family Tree DNA on their web sites. I have not found the list on Relative Genetics website, but you can see it by looking at the Barton or Rockwell test results.
Question
Another member asked a more specific question:
My mother and my uncle are the children of a Sturdevant. Their mother was the daughter of William E. Sturdevant, whom is the son of John W., who is the son of John S. Sturdevant. This family are the decendants of Addison and Elizabeth Sturdevant. Now, tell me... Will the DNA test work for my uncle to take? Or does it mess it up with him being born from a daughter of a Sturdevant? Should my mother do one of these tests?
Answer
This particular test, no.
This first round of testing is for direct male descendants. the y-chromosome is only passed from father to son. Your uncle will have the y-chromosome of the surname that married their mother.
Have you checked to see if there is a project already done with that surname? I would be interested if it has, in how the findings coincided with what you knew from genealogy.
As for testing your mother, it depends on what you are trying to find out, but probably not. Assuming you are trying to determine the heritage of Addison(?). Your mother and your uncle will both have the mtDNA that the wife of William E. Sturdevant passed on. It is hard to describe in words, but while the mtDNA is passed from mother to all children, only the female children pass it on.
You can SEE this process here:
