Ancestry DNA: Siblings With Different Results

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Can siblings have different Ancestry DNA results?  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? 

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!

Full siblings will show more similarities

If you and your sibling are full siblings, you will notice that your DNA results are similar, with slight differences. Half-siblings might find more noticeable differences, and this will depend on the ancestral background of the parent that they do not share in common.

The first thing to check when you are comparing your DNA results to that of your siblings is the number of shared centimorgans (cMs).  The number of centimorgans that you share with your match is visible directly on your DNA match list, as seen in the example below:

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. These are the general amounts of centimorgans shared between full and half-siblings:

• 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, unique features of Ancestry DNA results, 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.

It should be noted that ethnicity results should never be used to determine paternity, or evaluate 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.

Can full siblings have different DNA results?

Yes, it is absolutely normal for two full siblings to have Ancestry DNA results that are not identical.  In fact, would be more notable for two non-identical twin siblings to have identical DNA results.

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 almost impossible for two siblings to have inherited the exact same 50% from each parent. There is significant overlap of shared DNA, which is why we do see that siblings share a large percentage of their DNA with each other.

This difference, and overlap of shared DNA, 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. Since your sibling inherited the same percentage of DNA from each of your parents, you will see that they inherited a larger percentage of certain regions than you did.

The other really important 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 an approximately 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 you do, and vice versa.

And this is a perfect time to jump into the final topic of this post, which is that it is actually a really good thing when siblings take a DNA test and show different results.

It’s good that siblings don’t have the same Ancestry results

When our siblings take a DNA test, even if we share the same parents, we get the opportunity to learn even more about our ancestors than we could from just our own results.

The exception to this, of course, is if your parents are available and willing to test their DNA. This is always the preferable choice, since our parents (naturally!) have 100% of their DNA available to test.

However, many people cannot have their parents take a DNA test, which is why it’s a great idea for multiple siblings from the same family to test their DNA.

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!”   She said that I could just show her my results, and she could assume that our results would be the same.

After all, we have the same parents.

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

Eventually, 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.  My mother and four of her siblings have tested their DNA, 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. 

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:

• What is a Sibling DNA Match?
• Will my DNA Match My Sibling?

Conclusion

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.

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