Posted by Ancestry Team on April 23, 2015 in AncestryDNA, Guest Bloggers, United Kingdom

When I first took the AncestryDNA test, my friend Anna asked me if I had tested any other members of my family. At the time I remember thinking very clearly that I already had hundreds of matches, the last thing I needed was more matches. Fast forward a few months and my Dad mentioned he would like to do the AncestryDNA test. So as a birthday present I got him an AncestryDNA kit and he took the test. A few weeks later his results came back and he was very happy with the outcome. However for me it turned out to be one of the smartest things I’ve done since I originally took the test. Now when I get a match that’s also a match of my Dad I also know which side of the tree that match is on. It gets much easier to work out the shared relationship. I only have to compare our common match against half my tree.

I asked our ever helpful science team at Ancestry if they could tell me just how much of a benefit I get using both my test and my Dad’s. It turns out that with my test alone, the chances of matching a particular 4th cousin in the AncestryDNA database is about 71%. The reason for this is simply that each of us get different bits of DNA from our ancestors and by 4th cousin relationship there is a bigger chance we simply won’t match. But having both my test and my Dad’s test that number increases to 89%, much better odds. Not only that, the 89% is on Dad’s side of the tree. So I get a better chance of finding my 4th cousin but also more precision in working out a common ancestor.

That got me thinking of who else I should try to recruit on my cousin finding mission. Ask my sisters perhaps? Or should I try and get some of my cousins to test, particularly those who are on lines where I have brick walls. The answer to my question is shown in the image below.

Testing with family members

If I was to get any of my sisters to test it would boost my cousin finding rate from 71% to 83%. That’s certainly an improvement, but if I could get a grandparent to test that would increase my success rate from 71% to 98%. That 98% would also be in a specific quarter of my tree. This would be a huge increase in the success rate but also an increase in the precision because I am able to narrow down the match to my grandparents branches. I have no living grandparents, but I do have two grand aunts on different branches of my tree who are now top of the list of people I want on my cousin finding team. But what about my 1st cousins? I had considered asking some of them to test. Certainly it would increase my chances from 71% to 87%. But if I ask an aunt or uncle instead that number goes to 94%. And again, if both of us have the same match I can narrow it down to a specific half of my tree.

Like many of us researching our family tree I have spent many hours alone quietly in in libraries and archives poring over census documents or birth records. If there is one thing I’ve come to realise about doing my family history with AncestryDNA it’s that it is very much a team activity. The more people I can get on my team the better the results for all of us.



  1. Virginia Arsenault

    In looking into my ancestry I found I’m probably related to every white person in the eastern United States. Not that I’m totally disappointed, but I’d hoped to find a little more color. I know in a few generations, all of our descendants will look at pictures or we strange, pale people and think, ‘how odd’.

  2. toni

    This is one time when I would especially like to have a “printer friendly” button. I am trying to teach myself about DNA and it helps to have articles I find useful at my fingertips.

  3. All your promotions this week have finally talked me into buying some DNA kits to get tested for the first time. This post (after I shared it on Facebook) helped me to persuade both my parents and one male cousin on my Mom’s side to get tested too. Thank you for this posts and this graphic. I also wanted to tell you that I’ve included your post in my NoteWorthy Reads post for this week:

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