30 August 2019

This DNA Reference Site Solved a Mystery

Watch me solve a DNA mystery right before your eyes. I'm still in shock!

Is your DNA match list driving you crazy? I have so many matches I haven't figured out yet. It's time to look for help.

Here's my recommendation: Bookmark the Wiki of the International Society of Genetic Genealogy (ISOGG). There's so much to learn…so much you don't even know you don't know.

Autosomal DNA

I see people tossing around genetic terms all the time, and I don't know what they all mean. Take "haplogroup". I don't know which haplogroup I belong to. With a little bit of searching on Ancestry, I found that my Ancestry DNA test does not include my haplogroup. Whew! At least there's a good reason why I don't know my haplogroup.

Ancestry DNA looks at your autosomal DNA because everyone has that. It isn't restricted to only male ancestry or only female ancestry. That means you can potentially connect to more relatives with an autosomal DNA test.

Go to the Autosomal DNA page on the ISOGG Wiki and you'll see that several other well-known companies also offer an autosomal DNA test. You'll find a video on that page that gives you a quick background on how to make sense of your list of DNA matches.

The video includes a breakdown of how much DNA you should share with a parent, sibling, 1st cousin, 1st cousin once removed, etc. There are several charts available to help you make sense of the number of centiMorgans you share with your DNA matches. Here's a good one from Family Tree UK.


Let's talk about centiMorgans. That's the "cMs" your DNA site says you share with your DNA matches. Here's a simple—and wildly handy—way to see the percentage of DNA you share with someone. On the ISOGG Wiki page for centiMorgans it says to take the number of cMs you share and divide it by 68. That sounds crazy, doesn't it? 68?

I went to my DNA match list and picked my father. We share 3,441 cMs. Guess what that is when you divide it by 68? It's 50.6%. Bingo, he's my dad-o. My mom and I share 3,482 cMs. That works out to 51.2%. No wonder I look more like her.

I have a 1st cousin who has DNA-tested. As 1st cousins, we should share about 12.5% DNA. Using the "divide by 68" rule, he and I share 11.66% of our DNA. Definitely a 1st cousin.

This is how Ancestry DNA and other sites determine your approximate relationship to someone. Applying that rule, let's look at 2 of my most intriguing DNA match mysteries.

Mom's DNA Match

Mary is a match to my mom and me. She has no family tree online, so I wrote to her. Mary and mom's shared cMs work out to about 3.6%. Consulting the Family Tree UK chart, they could be:
  • 1st cousins twice removed, or
  • 2nd cousins
That's pretty close. After writing to Mary, I learned her DNA test gave her the news that her father wasn't her father. She told me the last name of her birth father, and I recognized it right away. That name comes from my maternal grandmother's parents' hometown in Italy. It's a small town, so I'm familiar with most of the names there.

My mission now is to help Mary by finding her connection to my great grandparents. Then, at least, I can give her a family. There aren't a lot of records available from that Italian town, but if I start pulling out everyone with her father's last name, I should be able to build something.

Dad's DNA Match

Linda is a DNA match to my dad and me and shares our last name. I wrote to her and her information was confusing. She said her grandmother was Rosaria Iamarino, but that must be her married name. She said her family has some roots in Argentina. Ancestry DNA estimates that my dad and Linda are 1st or 2nd cousins.

How can we not know our relationship?

In some DNA cases, you may simply need to look at your tree in a logical way.
In some DNA cases, you may simply need to look at your tree in a logical way.

Turning back to the "divide by 68" rule, Linda and my dad share 5.47% of their DNA. That's an in-between percentage that doesn't fall nicely onto the Family Tree UK chart. But there's a good chance Linda is my dad's 2nd cousin twice removed or so.

Looking at the shared last name of Iamarino, my grandpa had no brothers. And even though my grandmother was also an Iamarino, her brothers are legally named Marino. (Some crazy clerical error.) That means Linda's Iamarino grandfather may be the child or grandchild of one of my father's great uncles—one of the brothers of 1 of his 2 Iamarino grandfathers.

And now my brain hurts.

Maybe a visual aid will help. I'll look at dad's 2 grandfathers in my family tree: Francesco and Pasquale Iamarino.

Pasquale Iamarino had only one brother, and he died as a toddler. That rules out my dad's mother's side of the family.

Francesco Iamarino had 2 brothers. Giuseppe emigrated to the Bronx and stayed there for the rest of his life. My dad remembers him. Teofilo seems to have stayed in Italy. But something strikes me. I know Teofilo's son Gennaro moved to Argentina. And, oh boy, his son has a wife named Rosaria!

When I saw this couple's photo, I remembered something crucial. Argentina!
When I saw this couple's photo, I remembered something crucial. Argentina!

I learned this in January because Rosaria's daughter, my 3rd cousin Maria, contacted me from Argentina. As I look through our online conversation from January, Maria did say her brother lives in America.

Wow, the visual aid really helped. Linda's father should be my 3rd cousin. And now my Argentinian 3rd cousin Maria has confirmed it!

The Ancestry DNA estimate was only a bit off. Linda (my 3rd cousin once removed) is my dad's 2nd cousin twice removed. (OMG! That was my guess above.) She and her father are going into my family tree right now. I've just figured out this mystery, right before your eyes!

It's entirely possible Linda has some extra cMs in common with me because of my convoluted, complex relationship to her grandmother Rosaria's family.

Learn from this wild experience. An expert resource or two, and some logical, brain-numbing thinking, can solve your longstanding DNA mysteries too.


  1. DNA Painter is also a great tool to help you make sense of your DNA matches. One of the tools gives you an estimate of how you might be related. You put in the number of CM's and the tool tells you the probability of your relationship to that person. Here is the website.
    https://dnapainter.com/ You need to click on the Tools tab and pick "Shared CM tool". Plug in the number of shared CM's and get a great visual chart.

    The "painting" is awesome but that is another topic. I love the quick divide by 68 rule. excellent tip.

    1. I agree, and I have used and written here about DNA Painter. But that didn't do what I was able to do here. I narrowed down the type of relationship, and I knew I had to follow my maiden name. We should always be using all our tools!

  2. Agree. I always find it exciting to figure out how someone fits in my tree. I have the Wiki bookmarked now. I usually use a few different tools to help me along the way. The family inter marriages can be killer to my brain when I am trying to unravel connections.

    Besides the CM tool at DNA Painter site there is a tool where you can run scenarios to see how a relative might fit in - the "What are the odds" tool.

    I actually have my Genealogy favorites sorted into separate folders because there are so many useful Genealogy tools online. At the Wiki you cite there is a page devoted just to autosomal DNA tools - https://isogg.org/wiki/Autosomal_DNA_tools.

    I guess this is why I never tire of working on my Family Tree.

    I have found tons of useful information in your blogs and appreciate your help so much.


  3. I have a mystery similar and know which side of the family, nothing fits tho, I’ve even eliminated 4 siblings because there half brothers and my 2 nd cousin has dna from the second wife. So I’ve used dna painter, we have a lot of dna matches and still can’t pin point her grandfather. Her grandmother hide and changed names on a lot of things so documents are not helping. My conclusion is my grandpa had a son before marrying my grandma he was 31 at the time they married so it’s possibly, maybe he didn’t know about his son maybe he has a different last name, or given up for adoption. My sister thinks it’s his brother , he was married twice and no children. So far we don’t have any other unknown matches. My second cousin and I match other family matches as the same percentage so I think that’s why I am leaning towards a mystery son. If anyone wants to take a look at the dna painter I have, another set of eyes is always good!