Blog 2021 10 22 Are you waiting to understand the science of DNA before using it?

I have given several presentations this year about using DNA as just another genealogical tool.  I start by asking how many of them drive AND can explain the science behind the internal combustion engine of their car.  Very few know the science but they drive anyway.  Why?  Because they do not need to know the science to use the car as a tool to get from one point to another.

It is the same with DNA.  If you begin using it as a basic tool in the genealogy tool kit, you will become more comfortable with it.  The more comfortable, the more you start learning new methods to apply it.  It really is that simple.  Just like the auto have various types such as sedan, coupe, convertible, cross-over, and SUV; DNA has three types.  An explanation of each type will help you decide which one to use, or can use, and where to test.

Autosomal DNA (atDNA):  All DNA testing sites utilize the atDNA as the basis of their marketing.  The atDNA test can be taken by anyone and except for close family members: parents, children, and full siblings, the remaining DNA matches are placed into potential categories based on shared centiMorgans (cMs).  I will not fully explain cMs here, except to say that the more shared cMs, the closer the relationship, particularly if there are more and larger shared segments.  Just like gasoline, the more you have, the better off you are.  The atDNA results are good to about the 5th or 6th generation, then the number is so small as to be virtually unusable.

Mitochondrial DNA (mtDNA):  The mtDNA reflects the straight maternal line with virtually no change (mutations) for up to 52 generations.  Anyone can take the mtDNA to identify their mother’s line.  Therefore, if someone takes the mtDNA test the results will completely exclude the father’s family.  This test is currently given only by FamilyTreeDNA® at (FTDNA) and is quite expensive.  I personally do not recommend taking the mtDNA if money is tight unless there is a specific brick wall where the test results might be beneficial and the unknown matriarch is within six generations.

Y-DNA Test (Y-DNA):  The Y-DNA reflects the straight paternal line with almost no change (mutation) for up to 25 generations.  Only men can take the Y-DNA test and the results will identify the father’s family to the exclusion of the mother’s family.  This test is currently only given by FTDNA and the cost is less than the mtDNA.  The more markers (points on the chromosome) that are tested, the better.

Understanding centiMorgans (cM):  As stated, I am not explaining what it is, just how to use it.  When your results come back from most testing companies it will not show you have a specific relationship such as Aunt, Uncle, 3rd Cousin once removed.  But several possibilities unless the relationship is a sibling, parent, or child.  It will also report the amount of shared cM and perhaps the largest block or number of segments.  By using the shared cM number and comparing it to the Shared cM Project table listed below, you can begin to see where this person might fit in if you otherwise do not know.

The Shared cM Project:  Many people in the genetic genealogy arena, including Blaine T. Bettinger, and others, put together some great information to help people understand shared cMs, segments, and other DNA results and can be found at

What is meant by the cM range, is that you still have to do some traditional research.  Let’s say you share 1,400 cM with someone.  Based on that chart, this person could be Great Aunt/Uncle, Aunt/Uncle, 1st Cousin, Half-Sibling, Grandparent, Grandchild, or Great-Grandparent.  You must determine the reality.  I have two matches, they are siblings but one I share 383cM with and the other 283cM.  Since I know that they are both 1st Cousins once removed, that is where I put them and not as 2nd and 3rd as suggested by the testing company. has the largest database, by far, for the atDNA matches.  You can test there and download your raw DNA and then upload, for free, to FTDNA, MyHeritage, and GEDMatch.  GEDMatch is not a testing site but a third-party tool that allows you to compare DNA results regardless of where people were tested.  Do not be overwhelmed if you end up with thousands of matches.  Just work your way from immediate family and Aunts/Uncles and Nephews/Nieces, to 1st cousins, then 2nd, and so on.

Good luck and have fun taking DNA for a test drive.

Start using it and begin feeling more