DNA Questions

[crockettAdmin]

I had some questions about DNA results, so I wrote to Terry and she replied.  I am posting my original questions and her answers below.  This project is very worthwhile.  Thanks to those who are doing all the work. 
Hi, I am very interested in the Crockett family testing which is now beginning.  I just want to clarify a few things for myself.  There are five families of Crocketts with Virginia origins--Samuel, Joseph, David, William and Robert.  Now a couple of questions--

Hi Elizabeth.  Astute questions.  Answers by paragraph number:

1. Good idea to ask

If two men, say Samuel and William were brothers, they would share DNA.  So, if a contributor to our DNA database shared that DNA, we would know he belonged to that line but we could not know whether he descended from Samuel or William.  Is that correct?

2. Correct, in general, we would only know that all three share a common
ancestor.  The common ancestor could actually be from centuries before, or
be a father/grandfather.


If so, then determining that a contributor has a common DNA with one of the five Virginia Crocketts, say David, would not in itself mean that the contributor was a descendant of David's because he also might descend from someone else with the same DNA.  He might for example descend from some brother of David's.  Is that correct?

3. . Correct, he could even descend from a 10th cousin of Davy's

In fact, if it should be the case that all the five Virginia Crocketts are brothers, then a contributor who is found to share their DNA could tell he descended from their common ancestor, but could not tell which man was his ancestor?  Is that correct?

4. Correct.  He could even share their dna and not be descended from any of
the 5 brothers.

On the other hand, if a contributor does not share DNA with another contributor, they do not descend from a common ancestor.  If one of the two is KNOWN to descend from a given ancestor, it would mean that the other is not a descendent of that ancestor.  Is that correct?  If so, it would seem that it is of the utmost importance that we keep in mind that some links to ancestors are virtually certain and others are only probable.  For example descendants of the famous Davy Crockett are known with more certainty than descendants from some of the other families.  If we begin incorrectly believing that a given link to an ancestor is proven, we could undermine all our interpretations.  Is this correct? 

5 Correct.  Then the question comes in whether there is no match because the
two families weren't really kin or whether one branch had a "non-paternity"
event which causes a different DNA to surface (different from what the paper
trail should have produced)

6. Now for the flip side:

A. It is possible that the Crockett family will exhibit mutations which can
lay out some branching within the family, if they share a common ancestor at
some earlier stage.  This might allow us to identify descendants of some of
the 5 Virginia "brothers" by dna.  Or, ditto, some other Crockett families.

B. It is possible that all of the southern Crocketts will share a common
ancestor and that we won't be able to make any distinctions (I have this
problem in Barton)

C. To confirm the dna of a man who is no longer living, you need to test a
descendant of two differnt sons and get a match.  Until you have that, there
is always some speculation.  (But once you have identified a family
"standard" result, a single test is usually sufficient.

D A perfect scenario would have two sons represented for the earliest known
ancestor of each of the five VA Crockett families and each would have some
distinctive mutation which would identify them,  Then, all could be from a
common ancestor, or they could be from up to 5 separate genetic families and
we could still figure out who the Crockett families whose pedigrees stop
short of the mid 1700s descend from.

Thank you for your help. I find this project really exciting and think we will learn many things which will help us understand the relationships in the family. I just want to be clearer about how to be careful in interpreting results.  Elizabeth Smith posted these questions to the Crockett List. Thank-you Elizabeth for your questions.

[Biscuits]

I'll try to get these questions added to our Frequently Asked Questions page.

By the way, Terry is a he, not a she :)  It's one of those names that can be either male or female, so it can be misleading.

-Biscuits