Comparing DNA Results: Three Match Lists

It’s time for more DNA comparisons! This week I am exploring the Ancestry DNA results of three siblings by examining their DNA matches. If you missed last week’s post comparing some of the other aspects of the same trio’s Ancestry DNA results, you can click this link:

[Comparing DNA Results: Three Siblings]

In last week’s post I made the claim at the end that I thought testing all these siblings (at significant expense) was worthwhile because I had found new matches from each additional test. I thought this week would be a good opportunity to back up that claim with some numbers! It’s a long one so grab some popcorn…


Step One

To tackle this problem, I went through the first page of each child’s DNA matches, which displays the top 50 matches. For each match on the page I listed the number of centimorgans (cMs) shared with the child and the number of matching segments shared with the child. The first-page matches for each child appear in white in the chart at the bottom of the page. Since I didn’t include the siblings, themselves, in any of my counts, we can actually consider that I examined their 48 highest matches. This includes an aunt and an uncle of the children for whom I also manage the results.

I ended up with a total of 90 unique DNA matches that appear on the first page of one or more siblings. That means the children had some overlap within their top matches, but each one also had some DNA matches that did not appear in the top matches of one or both of their siblings. Let’s break down the match count a little:

  • 17 matches appeared on the first page for all 3 siblings
  • 1 match appeared on the first pages of both Child A & Child C, but not Child B
  • 11 matches appeared on the first pages of both Child A & Child B, but not Child C
  • 6 matches appeared on the first pages of both Child B & Child C, but not Child A

Just from these numbers, it’s already apparent that testing only one of the three children would have resulted in missing one or more “top” matches.

Step Two

With the first round of my list complete, I went back through and identified the amount of shared DNA for each sibling with each match, even if they didn’t appear on the first page for that child. I accomplished this by viewing the match page of each first-page match and clicking on the username. That brought me to their profile page (see image below) where I could select a DNA test I manage and it would either inform me it is a match to any tests they manage or it would say they were not a match. If they were a match I could view the match page and extract the shared DNA amounts, those numbers appear in gray in the chart. If they were not a match I put zeros in both gray boxes.

  • 4 matches were on the first page of only one child and had no shared DNA the other two children
  • 32 matches had no DNA shared with least one of the children but were on the first page of at least one child
  • 24.7 cM is the average difference in the amount of DNA each sibling shares with each of the 90 matches (calculated by finding the absolute value of the differences between all the columns and averaging it)
  • 192 cM is the largest difference in shared DNA between two siblings and a first-page match, excluding the aunt and uncle (Child A shares 192cMs more with Match 001 than Child C does)
  • 77 cM is the largest amount of DNA shared between a sibling and a first-page match that also has no shared DNA with at least one sibling (Match 067 and Child C share 77cMs, Match 067 shares no DNA with Child A)
Clicking on the match’s username takes you to their profile page where you can check if any tests they manage match any tests you manage.

Step Three

Next I sorted the matches from largest to smallest cMs for Child B. I decided to do this because Child B was the first to be DNA tested. This allows me to determine the value added by testing the additional siblings. What I discovered was that, within only these three first pages of matches, there were 23 matches that either would never have shown up on Child B’s match list (0 cMs) or might have been overlooked due to their small shared amount (~15cMs or smaller). These have been highlighted with a red box around them at the bottom of the chart.  Of those matches, 15 shared no DNA at all with the original test taker, Child B. Remember, we’ve only examined 90 DNA matches, between the three children there are thousands of matches. This, again, proves to me that additional siblings do bring something to the table when it comes to DNA testing!

Step Four

Finally, I took a closer look at the group of 23 “added” matches one by one and what I found was that many had potential to add significant value to my research. Below are a few examples of how some of these might contribute to my research (the examples are also highlighted in red font in the chart):

  • Match 067 had a very unique surname in their tree that is a huge research interest of mine. I am trying to work on a One Name Study for this surname and it has become a brick wall in my tree. This was a very important match for me that would have been totally overlooked without Child C’s DNA.
  • Matches 071 & 083, despite having very small trees, had a particular small town in both of their trees. I am almost certain I know which lines they will connect through if I extend their trees and communicate with them. It could help me get past some periods of poor records that have hindered my research.
  • Match 088 had both a surname and location that I recognize in their tree. Getting in contact with them could yield new stories or photos that I have been lacking on this line.
  • Matches 070 & 079 have large private trees. Getting in contact with them could open up new avenues for research.

These examples demonstrate that even though many Ancestry matches will have no tree or a private tree, testing addition siblings can reveal some new matches that do shed light on my research.


Although many of the matches in this list do appear somewhere in the match list of Child B, testing the other two children still helped me identify some close DNA matches. Ancestry does not make their match list easy to navigate. With limited search capabilities, limited ability to view shared matches, no option to re-sort the list, the shared cM amount not visible within the list, and now no page count visible on the list, even genealogically close matches can get buried beneath hundreds of pages if the amount of shared DNA is low. Low amount of shared DNA with one child can give the false impression that the match is quite distantly related and therefore not worth pursuing, when in fact the DNA of another child reveals the match is quite closely related. Sifting through page upon page of matches to locate useful information will tire even the most enthusiastic and dedicated researcher. Testing siblings allows some significant matches that would have otherwise been missed to float to the top of the list. This is the power of testing multiple siblings.

Let me reiterate that this analysis accounts for only a small sampling of matches. Imagine going through hundreds of pages where amount of overlapping DNA between matches and siblings become smaller and smaller. The value of testing siblings only increases. Additionally, each sibling has Shared Ancestor Hints, matches with public trees, and matches that respond to messages who are not represented within their first page but are still “value added” matches for my research.

It’s impossible to guess in advance how much value a sibling test will add to your research but the point is that you won’t know until you try it. If you have hesitated to test your siblings, your aunts and uncles, or multiple cousins, I hope you see that there is more to be found from genetic genealogy than what one person’s 23 pairs of chromosomes can tell you. You never know what brick walls might be solved by getting one more person in the family to spit in a tube!

With that in mind, the holiday season is fast approaching and DNA tests will be going on sale soon. My favorite way to buy AncestryDNA tests is to wait for the Black Friday sale. For the past 2-3 years Ancestry has dropped their price to $59 per kit, which is the lowest price of the year (outside of RootsTech, if you’re going to RT definitely buy your tests there). On top of this sale you can sign up for Ebates. If you don’t know about Ebates, essentially you begin all your online shopping trips through Ebates site. If you use their search feature to direct you to Ancestry’s website you can earn a percentage of cash back on your purchase. Typically this is around 6-10%, but often that number will increase, even double, for Black Friday!

Have you ever noticed a difference in DNA matches between relatives? Share your experience with me in the comments!

Behold the Giant DNA Match Comparison Chart:
(If the chart is too small to read you can view the full image here and zoom in on it.)


7 thoughts on “Comparing DNA Results: Three Match Lists

Add yours

  1. I have read this post with great interest. I seem to have something wrong with my setup for AncestraDNA. When I originally set up up this my account in 2001, it was done under my husband’s name, since at that time there was some worry about female’s security. Because so much history links to it, I have kept it the same through all these years. So when I sent in my sample and a couple other family members samples to be tested, they were all set up under their initials[administered by my husband’s name on account]. Since then I have also been given the collaborator rights on a couple more trees. One thing more, I tried to add my picture to my dna account and it has ended up being the profile picture for the account in my husband’s name. I add this as it might give you a clue to what i am talking about. Okay, now when I hit on any match on any of the dna accounts, it always comes up saying that the person “is not on your DNA match list”. The picture shown is not the avatar for each of DNA accounts but the profile picture of the main account and of course he has not had dna done as he is no longer living.
    So I cannot make use of any of the tips you have provided for this blog. Can you possibly enlighten me as to what I may have done wrong when I set up my family’s dna accounts? It not I appreciate that you took the time to read my long email to you and hope you understood it.
    Sandra Chester

  2. It’s impossible to guess what a sibling’s results will add to your research but you can expect about 50% more matches with the first sibling. The yield diminishes with each additional sibling but if you have the opportunity to do so, I would recommend testing at least 3 siblings (total of four). Testing the niblings can be very helpful as well if you are interested in phasing.

  3. Yes, this is what I had found in my research before testing all the siblings. Unfortunately, checking how that theory holds up against this set of siblings will either require more sophisticated analysis tools or more work than I have time for. But it would be interesting to find out!

  4. That’s interesting, I’m thinking of getting my half siblings tested when I have the money. We have the same dad but different mothers. The other interesting thing is that the eldest 4 half siblings our dad and their mum are first cousins so am curious how much they are going to match me.

  5. I have two siblings tested- my mother and her brother. I just got around to do the comparison of their first page of matches, and it was very revealing. My Uncle had several LARGE matches that my mother did not. One was 73 cent- 4 seg, another was 68 cent with 2 seg, I could go on. Very good reason to test as many as you can.

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