DNA is just DNA, right? So why have you been told to DNA test your oldest relatives?
Yes, any and all DNA will help you piece together your family’s history, however, some DNA is “more helpful” in this task than others. Let me explain.
Imagine a history textbook, like the ones you (most likely) had to buy for a college class. It’s heavy and has a couple of hundred pages of reading and illustrations. Now imagine this history book belongs to your grandmother and she passes it on to your mother. But, before your mom inherits the textbook, grandma rips out half of the pages at random! Your mom still has half of that history book, it’s still heavy and still has the same quality of content—the words, dates, stories, and images—but the stories are now incomplete. To continue the family tradition, your mom now passes the history book on to you, but just like your grandma, she rips out half of the pages! You have half (50%) of the textbook your mom had, but only one-quarter 25% of the textbook your grandma originally had. Sure, you can still flip through the pages and piece together the history that was originally in the book but it is not the same as the original textbook that your grandma had.
Now, instead of a textbook, think of your DNA. Your DNA is passed on, or inherited, almost exactly like the textbook from the analogy above. As DNA is passed from generation to generation you only inherit half of your DNA from one person, because the other half of your DNA comes from your other parent (one half from your mother and another one half from your father). So when we DNA test, our results will show that we have autosomal DNA from ancestors in the last six to eight generations. This means that your DNA can (usually) connect you to six to eight (6-8) generations before you. This means that if you DNA test your mom and it shows you six to eight generations before her that it will be seven to nine generations before you. Likewise, DNA testing your grandparent will have their results show six to eight generations before them which is eight to ten generations before you! Do you see now how DNA testing your oldest living relative can help you reach further back in your family’s DNA tree?
We’ll walk through an example with Ariel’s family. Ariel, her mother, and her maternal grandfather have all taken Ancestry DNA tests. All three of them share a DNA match. We’ll call this person, this DNA match, Sam (name changed for privacy).
Ariel shares 63 centimorgans (cM) of DNA with person Sam (as seen above). The amount of cM that they share helps us to estimate that Ariel and Sam are second cousins two times removed. Ariel’s mom shares 127 cM with Sam, which makes them estimated second cousins once removed. Finally, Ariel’s maternal grandpa shares 320 cM with Sam, which makes them estimated second cousins (share a set of great-grandparents).
As you can see, the DNA results from Ariel, her mother, and her grandpa give us much different information, because Sam is from the same generation as Ariel’s grandfather.
Can you see how DNA testing your target grandparent (the one you want to learn more about) is more helpful than your own DNA?
After reading the first part of this post, you may be thinking of an older relative who has not taken a DNA test. So how do you go about asking them to take a test?
First, you need to decide what kind of test you want them to take. As discussed in previous posts, we recommend Ancestry DNA kits because Ancestry has the largest autosomal DNA database. However, if you are conducting research along a direct patrilineal line or a direct matrilineal line, you may also be thinking about Y-DNA (patrilineal) and mtDNA tests (matrilineal). Whichever test you have in mind, be prepared to pay for it as a courtesy to your relative.
Next, you should be prepared to answer any questions your relative has about the DNA test. Most importantly, you need to explain why you want them to take the test and how it could help your genealogical research. You may need to explain how DNA is inherited—you can use our analogy above. Your relative may have privacy concerns, which can fall into a few different categories.
How is my genetic data being used and is it safe?
Ancestry outlines how they use genetic data in their privacy statement that you can read in full here. These uses basically boil down to genealogy and science. On the genealogy side, your data is used to generate ethnicity estimates and help you connect with your genetic relatives. On the science side, Ancestry uses aggregate DNA data to study populations and improve their DNA products. Ancestry will not share your genetic information with third parties except as outlined in their privacy statement or with your permission. For example, you can opt into the Ancestry Human Diversity Project, but your data is not automatically put into that project. Those third-party groups include insurance companies and employers.
What about the privacy of my relatives/ancestors?
A classic example of the desire for information clashing with the privacy of relatives is an adoptee searching for birth parents. Perhaps the adoptee is stuck in their search because their adoption was closed. Does the right of the adoptee to know their biological parents overrule the desire of the birth parents to remain unidentified? You may be going into DNA testing expecting no surprises. However, you should be prepared for the possibility that a DNA test will reveal private matters/secrets of relatives/ancestors. You should educate anyone you ask to test about this possibility. Discuss what you will do if family secrets are unearthed.
Does law enforcement have access to my DNA?
Perhaps you heard about how the infamous Golden State Killer was identified through DNA in 2018. DNA in that case was put in the GEDmatch, FamilyTree DNA, and MyHeritage databases which eventually led to the identification of DeAngelo through matches with family members. You can read about the use of DNA in that case here. This sparked a heated debate about whether law enforcement’s use of these databases breached the terms of service of those companies. While many people might be willing to let their DNA data be used to catch a criminal, the lack of consent was problematic. Most companies will not grant voluntary access to their DNA databases. To get a thorough breakdown of what kind of access different companies give law enforcement, read Diahan Southard’s blog post here.
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