Genealogy can be fun and rewarding, but it can also be frustrating when you encounter problems that don’t seem to make sense. What do you do if your family member’s DNA doesn’t seem to match your own? Legacy Tree Genealogists’ Adrienne Abiodun explains how you can solve this all-too-common problem.
Most of us who have taken a DNA test have experienced the startling discovery of NOT having a biological relative, close or distant, known to be related to show up as a genetic match. While jumping to conclusions and thinking the absolute worst is a natural reaction, taking a step back to assess the data or lack thereof may save you unnecessary confusion and heartache in the end. Siblings, half-siblings, aunts, uncles, nieces, nephews, first cousins, second cousins, and other immediate relatives should always share enough DNA to appear in genetic match lists across all major DNA testing sites. However, third cousins, first cousins, and second cousins that are two or three times removed may not always show up as a match.
For simplicity’s sake, let’s consider an example of third cousins. On average third cousins will share approximately 0.98 percent of their DNA, which is about 73 centiMorgans (cM) of DNA. Their shared DNA is inherited most recently from a great-great-grandparent or pair of second great-grandparents. From an individual standpoint, the amount of DNA one could have likely inherited from a great-great-grandparent is 6.25 percent, which is approximately 425 cM of DNA. Each ancestor generation backward, the amount of DNA inherited is reduced along with the potential of sharing DNA with known third, fourth, and more distant cousins.
On a recent complex client project, a non-match between two individuals who were supposed to be third cousins raised suspicions about their proposed common great-great-grandparents. If they did not share DNA, were they full third cousins, or could they be half third cousins? Were they even genetic relatives at all? A further investigation ruled out this last possibility but was insufficient to differentiate between the first two possibilities. Though they did not match one another, they both shared DNA because both matched with another relative from a third child of their most recent common ancestral couple.
Using the illustration below for reference, one can see a great-great-grandchild number one and great-great-grandchild number two were not genetic matches to one another. However, they are known proposed paper-trail third cousins to each other. Both matched grandchild number three and great-grandchild number three from the same common ancestor and shared an appropriate amount of DNA with those matches for their relationship types as first cousins twice removed and second cousins once removed, respectively. The most recent common ancestor pair would involve a marriage record that has yet to be found, a move from Finland to the United States of America where some children were born in Finland and some in the United States. The situation raises questions about whether child number one and child number two were half-siblings rather than full siblings.
In a situation like this, targeted DNA testing strategies were suggested and applied. A great-grandchild of child number two was invited to participate in DNA testing to determine how they would compare to genetic descendants of both child number one and child number three. Their DNA results were added to the analysis, resolving concerns regarding the genetic evidence. All three children of the most recent common ancestor(s) were, in fact, full siblings to one another. It also reinforced how third cousin matches may or may not share DNA. The relationship between the great-grandchild of child number two and great-great-grandchild number one is the second cousin once removed. The average amount of shared DNA for this relationship type is 1.64 percent or 122 cM of DNA. They shared 113 cM, which was very close to these observed averages.
In similar scenarios like this one, targeted DNA testing of additional individuals understood to be related to both DNA tested subjects in question is always encouraged when possible. But what if targeted DNA testing isn’t available? Here are some other strategies to consider for understanding your genetic non-match to your relative.
- Remain calm and attempt to refrain from jumping to negative conclusions.
- Determine whether you have calculated your relationship with one another appropriately. We will often hear two cousins refer to themselves as second cousins to one another when they are second cousins once removed, third cousins, or something entirely different from a second cousin. While it may all seem the same, in the game of DNA matching, precise relationships matter. Chart yourself and your cousin’s connection to one another and use relationship tools on sites like DNA Painter to understand removed relationships.
- If no test candidates are interested or available to pursue targeted DNA testing around the two individuals in question, sharing DNA match lists with your non-match to compare matches in common may also be sufficient. When sharing lists, observe whether you both have matches from your most recent common ancestor(s) and matches coming from both sides of your most recent common ancestors’ families. Evaluate whether the amounts of shared DNA with your in common matches is appropriate for their relationships to you and the distance between them and your most recent common ancestor.
In summary, it is essential to remember precise relationships matter when we incorporate genetic genealogy into our traditional genealogy research. More times than not, collaboration among your matches and non-matches is the key to successfully comprehending the data you do and the data you do not see.
DNA research can be difficult to understand, even with the right tools and resources. If you run into a problem you can’t solve, our genealogists will work with you to find the solution. Contact us today for a free quote!
The Shared cM Project 4.0 tool v4,” https://dnapainter.com, accessed June 2021.
Autosomal DNA statistics,” International Society of Genetic Genealogy Wiki, https://isogg.org/wiki/Autosomal_DNA_statistics, accessed June 2021.
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