The Importance of DNA to our Family History

Attendees at the Robbins Bicentennial Reunion in Indiana this summer had a great overview of the importance of DNA to Robbins family history by Greg Robbins of Florida.  I thought I’d provide a very brief recap to the discussion here along with my own thoughts.  Keep in mind: I’m no expert in this so others are welcome to share additional information or corrections in the comments.

It is that time of year when companies like Ancestry, 23AndMe, MyHeritage, and FamilyTreeDNA have sales on their DNA testing kits.  This usually happens around the family holiday season, as well as around Mother’s Day, Father’s Day, and DNA Day (April 23th this coming year).  If you are interested in testing your DNA this the time to get a kit at a greatly reduced price.

Why test your DNA?  The advertising from these companies is primarily focused on the ethnicity reports, that is discovering what region or country your ancestors came from.  This might be a disappointment to some as DNA is most accurate only to the continent level:  Europe, Asia, Africa, etc.  The testing companies constantly update their ethnicity results based on changes (updates to) their reference populations.  That is, they compare your DNA to others in specific areas (British Isles, Scandinavia, Southern Europe, etc.) to determine who you most match with.  The problem is that populations have not remained in one location over history.  The companies also change their groupings – Scandinavia gets divided into Sweden & Denmark as one category and Norway as another.  The results are interesting but I don’t find them particularly helpful for the type of genealogy I do.

The strength of DNA, as far as I am concerned, are with the matches identified between you and other testers.  Having a match with a distant cousin who claims descent from your probable ancestor helps cement that relationship and helps to prove out the paper trail that we were previously dependent on.

There are three kinds of DNA tests commonly available.  Autosomal (provided by Ancestry, 23AndMe, MyHeritage, and FamilyTreeDNA), and Y-Chromosome and Mitochondrial (only tested by FamilyTreeDNA.  The Y-Chromosome is passed down from father to son, so is useful with surname projects (i.e. Robbins surnames).  Mitochondrial is passed down from mother to children (regardless of gender) and can be useful similarly.  Autosomal is the DNA you inherit from both parents and is primarily that type that I have worked with.

As Greg mentioned in July there is a Robins/Robbins DNA Project based on FamilyTreeDNA.  This is most important for Robbins surnamed males – the idea being that they are descended, generation by generation, from other Robbins surnamed males and a compilation of the data will help sort out all the various s Robbins/Robins family lines.  I am not a Robbins surnamed male (my surname being Mittge) so a Y-Chromosome DNA test will not help me.  It is my understanding that the project can accept autosomal results but it’s much less refined, and thus less useful, than the Y-Chromosome testing, but I may try it one day.  I would encourage any Robbins surnamed males to test with FamilyTreeDNA and join the Robins/Robbins DNA Project.

I have worked almost exclusively with autosomal DNA results and primarily results through Ancestry.  I have also tested with 23AndMe and MyHeritage (as well as FamilyTreeDNA and a couple of others) but the data available through Ancestry is so large I’ve barely had time to move beyond that company.

You receive 50% of your DNA from your father and 50% from your mother, 25% from each grandparent, 12.5% from each great-grandparent, and so on.  Autosomal DNA is quite useful for a broad view of your genetic relatives but becomes less useful as you move back through the generations.  There is a point where you do not carry the DNA of particular ancestors because each child receives a random split of their parents DNA.  That being said, I have DNA matches with relatives who are fifth or sixth cousins, so obviously we each received some small amount of DNA from the same far distant ancestor.

Here is a chart from the International Society of Genetic Genealogy showing the likelihood of not sharing DNA with cousins as their relationship moves further away from you.  You will definitely match with a biological 1st cousin, while you have a nearly 70% chance of not matching with a 4th cousin (which still leaves a 30% chance that you will!).

The 50% autosomal DNA you receive from each parent can be somewhat different than the 50% that your sibling inherits.  That’s why it is important and very useful to test as many people as possible in your family.  Your sibling may inherit more of a particular ancestors’ DNA, while you may inherit more of another one.  You may match with a distant cousin while your sibling may not – it doesn’t mean they aren’t related, just that the bit of DNA from the common ancestor didn’t get passed to you or them. 

This chart shows four siblings with colored squares representing the DNA they have received from the parents, grandparents, and great-grandparents.  Each sibling is slightly different so testing each sibling is very useful for genealogy.

An example:  my brother shares much larger chunks of DNA with many of our Robbins cousins than I do.  He shares something like 147 cM (centimorgans, a unit of measurement of DNA) with one of our third cousins (another Robbins descendant), while I share 22 cM with the same person.  One of my brother’s matches, which I don’t share, is with a Robbins cousin who I believe comes down through the Chastain family – many, many generations away.  This is wonderful for sorting out and proving family lines.

I hope all of you consider DNA testing at some point.  It’s fun and extremely useful for family history research.  But –it’s up to you to test or not – you need to be comfortable with your decision – reasons not to test can include concerns about privacy, concerns about “surprises” you may not be comfortable with, not wanting to connect with strangers (albeit “biological” ones), and other reasons.  For me the decision to test was fairly easy, but we should all respect the choices of testers and non-testers alike.

And with that I would like to wish everyone a happy holiday season and a wonderful 2023!