DNA Testing and Results

DNA Testing Dodson and Dotson

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DNA Testing and Genealogical Research 

People have always had reasons to establish an ancestral lineage.  A desire to find ones roots might be a hobby, family pride, locating birth parents or a desire to join a patriotic organization.  So many errors have been made over the years with scanty or no documentation.  DNA is now debunking some family myths while creating some unanswered questions. 

There are complex DNA tests to solve crimes or establish paternity, but with DNA testing for genealogical purposes, the results will only show the probability of a most recent common ancestor.  

Since DNA testing only shows probable ancestors or relatives,  it does a better job of proving who is NOT your ancestor than who is your ancestor.  It does not remove the need for careful research to prove your line.  You will only learn of those that match, and only the amount of information that they wish to share with you.

The most common DNA test is called autosomal.  This test will match you to others who have some degree of relationship on either your paternal or maternal side.  This test is less accurate as the number of generations increase, while other tests can test a male or female line for an infinite number of generations. Three major companies perform autosomal DNA testing.

Autosomal testing is the only test performed by Ancestry and 23 and Me, but 23 and Me offers more health information.  Family Tree DNA can perform the autosomal as well as the other tests.   Millions of people been tested through Ancestry, so there is more probability of finding a cousin match there. In Family Tree DNA, you might have matches to males who have had the y-DNA test.  However, if using Ancestry, it's important to understand what to expect when you start getting your cousin matches - and how to make them most useful.  If at all possible, it's best to add your own family tree to Ancestry first, before the test, and also to make yourself the "home person".  That way, you will be able to see how you match others on their family tree when your results come in and also as new results are posted from other matches.    

An outline on How to best use your Ancestry results

Y-DNA Genealogy Test - What does it prove or not prove?

The y-DNA test  will show a continuous MALE lineage from a present generation male to direct ancestors with his surname.  All males who share a common surname can be tested to show their relationship or non-relationship to an ancestor with that surname or to other males of the same name.   In cases of adoption the surname may have changed but the DNA will not.  There is a similar test for women that will test their continuous maternal line.  

Based on the number of markers tested and the match of those markers, the probability increases, as seen in the charts below, but again DNA does not prove ancestry, it only establishes a relationship to others who have been tested and shows that you and that person probably share a common ancestor at some point in time. 

With more matches, the odds increase that there was a common ancestor within a certain number of generations, but if you achieve a perfect match on 37 markers, for example, the best you have is a guaranteed match within 480 to 720 years ago.  However, if 2 persons match on 67 of 67 markers, their common ancestor could be more recent. 

Probability Charts for Most Recent Common Ancestor (MCRA)  in Y-DNA testing

From Family Tree DNA Site

Number of matching markers 50% probability that the MRCA was no longer than this number of generations 90% probability that the MRCA was no longer than this number of generations 95% probability that the MRCA was no longer than this number of generations
35 of 37 6 12 14
36 of 37 4 8 10
37 of 37  (100%) 2 to 3 5 7
65 of 67 6 12 14
66 of 67 4 8 9
67 of 67  (100%) 2 4 6

DNA testing can quickly suggest the possibility of relationships, or those you should disregard, but documentation is still the only way to be certain.