If you and your sibling both did the Ancestry DNA test for fun, you might be confused over your results. If you are full siblings, why are your Ancestry DNA results different? Can siblings have different Ancestry DNA results?
Before you jump to any conclusions about mom or dad, you should definitely read this post.
In this article, you will discover:
- How much DNA is typically shared between full siblings
- Why is it completely normal for full siblings to have different Ancestry DNA results (or results from any other company, for that matter)
- Reasons for siblings to do a genetic DNA test, even if they share the same parents
By the way, don’t forget to check out my DNA Tools Page where you can find all of my most helpful blog posts as well as links to other great resources to help you get the most from your DNA!
Are You Full Siblings?
The first thing to check when you are comparing your DNA results to that of your siblings is the number of shared centimorgans (cMs). Read this article to see how you can access that information on Ancestry DNA).
Ethnicity results between full and half-siblings have different characteristics, so it is important to first determine the exact nature of your relationship with your sibling.
- Full siblings will share between 2300-3900 cMs.
- Half siblings will share between 1300-2300 cMs.
If it turns out that your shared DNA falls into the half sibling category, your DNA results will show some similarities, but also large differences.
For example, your half-siblings may have Migrations or Genetic Communities (Ancestry DNA concepts) that are very different than yours. They will have many close-distance DNA matches that you don’t have, and vice versa.
Even if your DNA falls into the full sibling category of shared DNA, your results will be different than your sibling’s. You will show slightly different ethnicity percentages, and even different DNA matches.
Note: I should also stress that ethnicity results should never be used to determine whether a sibling is a full or half-sibling, since it is very common to see big differences on ethnicity estimates. The easiest reliable method for figuring out whether a sibling is a full sibling or a half-sibling is to compare the shared centimorgans with the ranges that I mentioned above.
Is it normal for full siblings DNA results to be different?
Yes, it is absolutely normal for two full siblings to have Ancestry DNA results that are not identical. The DNA of two siblings should show a lot of similarities, but it won’t be exactly the same.
This might sound odd, since if you both share the same parents, why isn’t your DNA exactly the same? It’s because each of you only inherited 50% of each of your parents’ DNA. Just based on probability, it’s impossible for two siblings to have inherited the exact same 50% from each parent, which is why there is a lot of overlap, but still some difference.
This difference, and overlap, will show up on your Ancestry DNA results. For example, if you had a parent who had a high percentage of Eastern European ethnicity, for example, it’s likely that both you and your sibling inherited a big chunk of it.
The “chunk” might not be the same size, so you might have 34% Eastern European, while your brother has 29%, for example.
The other really importance way that the similarities and differences appear on your results is via your DNA match lists. You and your full sibling will share many matches. The closer the match, the more likely it is that it is shared by both of you.
In fact, you and your sibling will share all DNA matches until the 3rd cousin level. At the 3rd cousin relationship distance, there is a 10% possibility that you don’t share DNA with any particular 3rd cousin.
For this reason, it is possible that you and your siblings might have a few different 3rd cousin matches.
The differences in the DNA match lists will really become apparent at the 4th cousin relationship distance. There will be many fourth cousins, and many, many more distant cousins that you have that your sibling doesn’t have, and vice versa.
And this is a perfect time to jump into the final topic of this post:
Why it is good for more than one sibling to do an Ancestry DNA test
…. even if they share the same parents. I remember when I first did the Ancestry DNA test, my sister said to me, “Well, that’s good. Now, I don’t have to do it!”
At first, I thought that maybe she was right. The more I learned, however, I realized that it would be good if all of my siblings did the test. The more siblings test, the more “complete” the family history picture can be.
As I mentioned earlier in this post, you and your siblings each inherit 50% of your DNA from each parent. That’s easy enough to understand.
The cool part about testing more than one sibling (or several, if possible) is that each sibling has a little bit of DNA from each parent that the other siblings don’t have.
How amazing is that!? These small bits of DNA that now belong to each sibling, and are not shared by the others, contain valuable clues about the family’s past:
- Trace ethnicities that were not inherited by the other siblings
- 3rd-8th cousin matches that might help break down brick walls in the family tree
Both of my parents were able to do the Ancestry DNA test at my request. My mother’s parents, however, are no longer with us. She and four siblings have tested, and because of that, we have access to a wealth of information about our family tree.
It is a lot of work to go through all of those results, but very worth it (especially for someone who loves genetic genealogy as much as I do).
Since I strongly encourage testing siblings, I have posted the link below to make ordering another kit convenient for you.
You can use the link below to order your Ancestry DNA kit (I’ll get a very small commission at no extra cost to you – thank you so much): Discovery the story AncestryDNA® can tell I appreciate you helping me support the work that I do on this site.
For further reading, you also might be interested in these posts, which are also related to the amount of DNA shared between full and half siblings:
I hope this post helped you understand a bit about why you and your siblings have different results.
Did you find anything interesting out about your family when you or your siblings’ results came back? I’d love to hear your story in the comments!
Thanks for stopping by.