Do you want to know if DNA matches will be the same for siblings? If siblings have different DNA matches, what does it mean? In this post, learn the answers to these questions – and more.
When two siblings do a DNA test and notice differences in their DNA matches, it can cause significant confusion. Are the DNA results wrong? Are they really half-siblings?
We already know how and why siblings can have different ethnicity estimates or ancestry reports, and in this post, we will learn even more about how DNA is inherited. By the end of this post, you will know why it’s completely normal for some – but not all – DNA matches between siblings to be different.
If siblings don’t share a match, does it mean they are half siblings?
No. We can only determine whether two individuals are full or half-siblings based on the amount of DNA (centimorgans) shared between them and genealogical information. Full siblings will not share 100% of their DNA matches.
Why do siblings have different DNA matches?
When a child is conceived, they inherit 50% of their mother’s DNA and 50% of their father’s DNA. The 50% of each parent’s DNA that the child inherits is randomly selected in a process called recombination.
Each offspring that a couple conceives will inherit a randomly selected 50% of each of their parent’s DNA. The randomly selected DNA that one child inherits will not be identical to the randomly selected DNA of their sibling.
We generally expect to see two full siblings share between 32-50% identical DNA, with some full siblings sharing as much as 54%. The reason that full siblings don’t share 100% of their DNA is because of mathematical probability.
It’s just not possible for two siblings to inherit 100% identical DNA from their parents unless they are identical twins. Identical twins should have a fairly similar DNA match list.
If you and your siblings aren’t identical twins, definitely keep reading!
Since siblings share a lot, but not all, of their DNA, we can now envision why they will share most – but not all – of their DNA matches. The DNA that each sibling inherited from each parent that doesn’t match their brother or sister will be DNA that will match distant cousins.
How different are DNA matches between siblings?
Everyone shares DNA with their closest relatives. This means that two full siblings should always share the following DNA matches:
- Parents
- Full and half-siblings
- Aunts and uncles
- Grandparents and grandchildren, including great-grandparents and great-grandchildren
- First and second cousins, including first and second cousins once-removed*
* There is a non-zero chance of sharing no DNA with a second cousin once-removed, but it remains most likely that you share DNA with all of your second cousins once-removed
As we move further down our DNA match list, the possibility increases of finding DNA matches that one person has that their sibling does not share. For example, a person will share DNA with 90% of their third cousins.
This means that even though a third cousin is related to both siblings, it’s possible that one of the siblings might not share DNA with that cousin. Even so, we find that siblings will share most, or even all, of their third cousin DNA matches.
When it comes to distant cousins who are estimated to be related at a fourth cousin distance or greater, all bets are off. There is only a 50% chance that we will share DNA with our fourth cousins.
The result of this is that we will have lots of fourth cousin or more distant DNA matches that don’t match our siblings, and vice versa. This is one reason why it is very beneficial to have all siblings from a family do a DNA test, especially if parents are unavailable for testing.
There is a lot that we can learn about our shared ancestry from our siblings’ DNA results.
Can siblings have different false DNA matches?
Most of the people on our DNA match lists are indeed related to us in some way. There is a possibility, however, that some of the distant cousin matches on our list are false matches.
Conclusion
I hope that this post has helped you understand why full siblings won’t share 100% of their DNA matches with each other, and what it really means. If you have any questions about something that you read in this post, or if you would like to share your own experience not sharing a match with a sibling, I would love to hear from you in the discussion below.
Thanks for stopping by today!
Diane
Tuesday 7th of June 2022
If two sibling share different fathers the dna test will be different between the two per the fathers dna. If you are then unsure that they have the same mother due to differences in the dna test results for the mother, how do you find out for sure. How far off can the mothers dna results be to know if they do not have the same mother? Sort of like a switched at birth scenario.
Margaret
Sunday 5th of June 2022
This might be a bit off topic…. My husband and I tested our dna and 0% came back Italian for each of us. However, our daughter’s test states 20% Italian. Can dna skip a generation?
Mercedes
Friday 10th of June 2022
Hi Margaret, DNA can't skip a generation. What most likely happened is you and/or your husband have DNA from a region neighboring Italy, or not too far geographically. In certain cases, the algorithms can "confuse" DNA segments when they aligned in just the right way and seem like they are a different ethnicity. One interesting thing that you could try is downloading all of your raw DNA files and uploading to another site (there are a few that accept uploads) to see if a different algorithm reports slightly different results. What an interesting question! Thank you for your comment, Mercedes
Janet
Friday 3rd of June 2022
My sister and I did ancestry and her results say close family at 28% dna, 1985 cM, across 52 segments. Are we half-siblings??
Mercedes
Sunday 5th of June 2022
Hi Janet, We expect half-siblings to usually share between about 33-50% of their DNA, but there are occasionally exceptions. You might find this post helpful: https://whoareyoumadeof.com/blog/full-sibling-or-a-half-sibling-dna-details/ Best of luck to you! Sincerely, Mercedes
Clay Price
Thursday 17th of February 2022
I just had my sister and brother take a DNA test and I wondered if our lists of DNA matches would be the same. Your article was the one that actually answered my question. Looks like the lists will be identical until we get to 3rd cousins where there is a 10% chance of finding a different match--if I understand your article correctly. Very helpful so thank you for another insightful post, Mercedes.