I saw this on Ancestry.com – How Many DNA Tests Does One Family Need?: https://blogs.ancestry.com/ancestry/2019/04/23/how-many-dna-tests-does-one-family-need/.
The short answer is, How many people are in your family? If you’ve already taken the AncestryDNA® test, you may think you’re done. You could test other family members, but since you’re related, they will have the same results as you, right? Not exactly.
Both you and your biological family inherited your DNA from your ancestors, but like most inheritances, who actually ends up with what can get a little messy. It’s true, you share DNA with other members of your family, but each of you gets a unique mix and different amounts from various ancestors. So the closer you can get to a DNA source, and the more sources you can identify, the more you can learn about your family and grow your family tree.
You get half your DNA from Mom and half from Dad. One of the most powerful benefits of having their DNA tested is being able to assign your DNA matches to a specific branch of your family tree. Ancestry will now call out DNA matches as “Mom’s side” or “Dad’s side” for parents you’ve had tested. Also, getting them tested lets you dig into the half of their DNA that you didn’t get. Odds are they will have DNA matches that you don’t have. Imagine the possibilities!
If you’re lucky enough to still have living grandparents, having their DNA tested can pay even bigger dividends than testing your parents. Remember, not only does it allow you to assign matches to even more specific branches of your tree, but your grandparents’ DNA has mixed once since coming down to your parents and twice since coming down to you. So, while your DNA can give you high confidence matches 5–6 generations back, your grandparents’ DNA matches can connect 7–8 generations back from you with that same level of high confidence.
Unless you’re an identical twin, your siblings received a different mix of DNA from your parents than you did. While results can be similar between siblings, ethnicities can vary, and a sibling may also connect to DNA matches that you don’t. This may seem counter intuitive, but remember, DNA inheritance involves a great deal of randomness. Testing a sibling opens the possibility for you to discover new cousins and new insights into ethnicity and historical communities, especially if your parents aren’t available to test.
Aunts, Uncles, and Cousins
Your aunts and uncles have a significant link to you and can be a great proxy for, or supplement to, your parents’ and grandparents’ DNA. You will likely share similar matches, which can help determine which branch of your family tree a match belongs to. And like your parents, grandparents, and siblings, the matches you don’t share could lead you to new discoveries in your family tree. Plus, it’s a great way to get others in the family involved in your family research.
You may have a lot of things in common with your spouse, but DNA matches are not usually one of them. So your DNA test won’t help trace your spouse’s family tree. Having your spouse tested can also be lots of fun. You can compare your ethnicity results, see who gets the most matches, and share your findings with the rest of your family. If you have children, testing both you and your spouse’s DNA can help paint the picture of the heritage you each passed down to them.
While testing your children may not solve any genealogical mysteries for you, assuming you have already tested, it can inspire interest in their family story. A 2010 study from Emory University found that children who know stories about their ancestors had better coping skills and higher levels of emotional well-being. And who knows, you may be inspiring the next generation to take up the genealogical torch.
Things to Consider
- Test Older Relatives First. By testing the “oldest” DNA in the family tree, you get the strongest connection to the past. Consider this: a fourth cousin to you is a third cousin to your parent and a second cousin to your grandparent. Because the relationship is closer, you can go further back in time with more confidence by testing older relatives. And, sadly, our older family members are our most endangered. So it always makes sense to test the oldest living relatives in your family tree on each of your branches.
- Pinpoint new cousins on your family tree. Think of your family tree. It starts with you, then immediately splits into two branches: your paternal and your maternal relatives. You got DNA from both branches of that tree—but your parents didn’t. By testing multiple people on both lines, you may find more distant cousins that point to a relationship to a particular grandparent, great-grandparent, etc. Using shared matches, when you identify the branch of the family a cousin is associated with, you can create custom, color-coded groups to remind you how you are related. Testing gets really exciting the further back you can go.
- Find more cousins. Depending on who you test in your family, you could have some of the same DNA matches, which can give you clues about who the shared ancestor is for that match. But other family members may also have matches that you don’t, which could mean new discoveries in your family tree as well. Either way, it’s a win.
- Have some fun. Getting other family members involved in your family history research is just downright fun. You can compare your ethnicity results to see who got what mix of ethnicities or who has more matches on which side of the family. DNA is a cool new technology that can get the rest of your family more interested in their ancestors. Trust us; we’ve seen it happen.
So, now it’s your turn. Get started and get testing.
 Fivush, Robyn, Marshall Duke, and Jennifer Bohanek, Emory University, (Atlanta, Georgia). “Children Benefit if They Know About Their Relatives, Study Finds,” Journal of Family Life. Press release dated 3 March 2010. Emory University (http://shared.web.emory.edu/emory/news/releases/2010/03/children-benefit-if-they-know-about-their-relatives-study-finds.html: accessed 23 Apr 2019).