Robert Barton: DNA and Relationships

Going back just 4 generations to direct ancestors, each person has 16 2nd great grandparents (2 parents, 4 grandparents, 8 great grandparents, 16 2nd great grandparents), so very quickly you don’t share very much DNA with your ancestors. However, the shared segments and where they are on even a small percentage of DNA can tell us a lot, and can connect people who have shared ancestors. These connections are also an opportunity for sharing information and common research results (which is so important to genealogical investigations). Looking at Robert Barton’s autosomal DNA test, we can tell about his parents’ DNA, close and distant family matches, and hopefully begin to communicate with them. The charts below are from Robert Barton’s Ancestry.com autosomal DNA test results.

DNA From Which Parent?

Because autosomal DNA tests look at the chromosomes we inherit from both our parents, and we get half of our DNA from one parent and half from the other, companies can tell likely relationships between testers based on how much DNA is shared on which chromosomes, and they can tell which DNA likely came from which parent even if those parents didn’t take DNA tests. In this ethnicity graph, you can see Robert Barton’s DNA results and what he likely got from each parent—a lot of England/Northwestern Europe from both parents, more Germanic Europe and Sweden/Denmark from his father, and all of his Ireland from his mother.

Chart adapted from Ancestry.com, 10 Feb 2023.

Most people have 23 chromosome pairs, with one of each pair coming from each parent. The chromosome that each child gets is random, and children don’t get exactly the same 50% DNA from each parent—which is why we are not exactly like our siblings (not counting identical twins). The less matching DNA, the lower the relationship percentage shown by the DNA test. Using your submitted DNA and the submitted DNA of others, companies can also match sections of DNA to other people to determine if these “matches” are likely on one parent’s side of the family or the other (or on both sides if the match is descended from the same set of parents that you are (and a couple less common cases)), as well as what the likely relationship is.

Roughly, shared DNA means:

• 50% DNA is a parent/child relationship

• about 25% can be grandparent/grandchild/1st cousin

• about 10% can be 1st-2nd cousin/great grandchild

• about 5% can be 2nd-3rd cousin

In this photo, you can see Robert Barton’s DNA matches are to his daughter, with 50% shared DNA, and to two of his granddaughters, with 28% and 23% shared DNA. His great granddaughter shares 11% of his DNA. (Chart adapted from Ancestry.com, 10 Feb 2023.)

Shared DNA can also be measured in centimorgans (cM), which indicates the length of DNA segments shared with your relatives. Higher centimorgans indicate a closer relationship.  with the frequency of genetic recombination. You can also see the centimorgan measurements in the photo as well. Knowing the centimorgans can also help indicate relationships. I have included average centimorgans in some of the relationship table below. If you are interested in more about centimorgans as a unit of measurement, see here: https://www.familysearch.org/en/blog/centimorgan-chart-understanding-dna.

Looking at DNA matches with others, and their family trees (if they share them), can help to figure out missing ancestors, or to confirm research you have done. Percentage of DNA shared and centimorgans are one thing to look at, as well as any shared ancestors on your family trees—ideally finding your Most Recent Common Ancestor (MRCA). Knowing the MRCA allows you to define your relationship, and how you connect with other family members across generations. (And not generations as in Gen X, Z, or Millenial, but as in children/parents/grandparents each being a new generation of the family).  

Some generational relationships, we know easily – my sister’s children are my niece/nephew (one generation removed from me). My mother’s brother’s children are my cousins (we are the same generation). But beyond that can be confusing. Each column or row away from the Most Recent Common Ancestor (MRCA – top left corner) is a generation removed from the previous column—child, grandchild, great grandchild, etc. If you know the most recent ancestor you have in common with someone (the MRCA), you can use the chart to find your relationship. Find yourself in relation to the MRCA across the top, and find the other person down the side. Where your column and row meet in the table is your relationship.

Chart describing relationships based on Most Recent Common Ancestor (MRCA)

For example, my grandfather’s (Robert Barton’s) sister’s grandchildren are my second cousins. We share great grandparents (Robert Barton’s parents Lynn and Ava (Morgan) Barton), who are our Most Recent Common Ancestors (MRCAs). Reading down the column labeled “great grandchild” (me), and reading right in the row labeled “great grandchild” on the left, we intersect at “2nd cousin”—our relationship. We are the same generation – both great grandchildren of our common ancestor, and are 2nd cousins to each other. However, my 2nd cousin’s children (a generation removed from me and one row lower on the table), would be my 2nd cousins once removed.

Another way to use DNA, is to connect through messaging with relatives (close or distant) with shared DNA through the various platforms where your DNA has been submitted. Ancestry.com uses DNA and linked family trees to suggest “ThruLines” to note matches, who can then be contacted through the platform’s messaging. This chart shows some of Robert Barton’s DNA matches descended from William Slater – Robert Barton’s 2nd great grandfather.

Chart showing some of the “Thru-Lines” — descendants of William Slater who share DNA with Robert Barton (Ancestry.com, 11 Feb 2023)

Messaging distant relatives is a tricky thing to do, as not everyone responds or has any information to share. Many people take DNA tests but don’t do genealogical research, so you have to find the right contacts. I have only just started this. On Robert Barton’s line, through ancestry, I have messaged a second cousin with shared DNA (who did not respond), and a couple of fifth cousins (one with a shared DNA profile – connected on the Barton line, and one with a public family tree/no DNA test—connected through Robert’s Slater ancestors), to discuss small things, but we have not yet gotten into details.

I am hoping that my webpage can also prompt further discussions with people with shared interest in genealogical research into our shared ancestors. Although we may share just small amounts of DNA, there are a lot of generations of potential genealogical research that we share – an exciting prospect.