Who’s More Irish, You or Your Sibling? The Surprising Science Behind the Inheritance of Ethnicity

by Anna Swayne

Growing up I always thought I had to be more Irish than any of my siblings because I was born on the day before Lá Fhéile Pádraig (Saint Patrick’s Day)—one day early I might add; my due date was actually the 17th.

When I realized an AncestryDNA® test could tell me if I really was the most Irish, I jumped at the chance.

My DNA test results—compared to my sisters’ results—were completely surprising!

Ready, Set, Spit

I started by testing my own DNA. And my test results did indeed confirm my Irish roots. (Phew!)

Ethnicity estimate for Anna Swayne.

But my test was only half the story.

Yes, I was almost a quarter Irish. But was I more (or less) Irish than my sisters? To find out, my sisters needed to take a DNA test too.

Luckily they were easy to convince. They spat in the test tubes, sent in their saliva samples, and waited.

Who’s Most Irish: Can You Guess?

Though, as I had explained to my sisters, most siblings have a different mix of ethnicities due to the random nature of genetic inheritance, I still wondered: How different could we really be?

And of course I was dying to know: Which sister would prove to be the most Irish?

As we waited for our results, we challenged our friends and family to see if they could tell who looked “most Irish.”

Can you tell just by looking at us? Here we are, from oldest to youngest (that’s me on the far right).

Portraits of all four sisters.It’s hard to say just based on our photos, I know. We don’t even look particularly alike, though I can say for sure we are all sisters — DNA did prove that.

And the DNA Verdict Is…

After several weeks, we had everyone’s results.

Take a look:

Ethnicity estimates of Swayne sisters highlighting Irish DNA.

Do you see what happened? My oldest sister’s ethnicity results (on the far left), show she’s 45% Irish.

Mine show I’m just 22% Irish. So my sister is twice as Irish as I am!

And my other two siblings were right around 30% Irish. That means, despite my birthday, I’m actually the least Irish.

I Was the Odd Woman Out

Oh wow. I was reeling. But our DNA had more surprises in store.

Take another look:

Ethnicity estimates of Swayne sisters highlighting Western European DNA.

All three of my sisters received a good portion of ethnicity from Europe West — and I basically got none.

In the first moment I almost felt robbed. But then I realized my ethnic mix is just different but every bit as awesome.

I am, for example, the most British (cue British accent and Britishisms like “Bob’s your uncle”).

How Can This Happen?

We all get 50% of our DNA from each of our parents. But they don’t give each kid the same 50% — unless you’re identical twins.

So it’s not super unusual for siblings to have different percentages of their parents’ ethnicities.

It makes sense if you think about the science behind it. But the first time most of us learn that our siblings can be more Irish or have DNA from a region that we totally lack, it’s definitely mind blowing.

Are you more or less Irish (or any other ethnicity) than your siblings? Find out with an AncestryDNA test.