Sunday, 29 November 2020

Ancient Irish DNA (or lack of)

'Do you share DNA with any of the four ancient Irish samples on GEDmatch?' asked Margaret O'Brien of Data Mining DNA recently.1
Unlikely, I thought, given they lived four or five thousand years ago and I don't even share DNA with some known third cousins. But wouldn't it be fun to investigate!

GEDmatch is a 'free' third-party DNA site, where people who have tested with various testing companies can upload their results and compare them to each other. The results for the four ancient Irish people have also been uploaded, so it's easy to run the comparisons.

Ballynahatty Woman
DNA analysis on the bones of a Neolithic woman discovered in Ballynahatty, near Belfast, Co. Down, reveals that genetically she most resembles modern people from Spain and Sardinia - not Ireland. It is estimated this woman lived here over 5,000 years ago. Her ancestors originated in the Near East. I didn't expect to have any real matching segments with Ballynahatty Woman, so the normal minimum threshold level of 7cM was reduced to a just 3cM, so there might be something to see. And, here are the results:-


I have four matching segments greater than 3cM with Ballynahatty Woman, the largest being only 4.7 cM. Segments this small are notoriously unreliable, meaning they are most likely identical by chance. And it's a total coincidence I share any DNA with Ballynahatty Woman.

As you can see, neither my mother nor father share these matching segments with her, and I inherited ALL my DNA from them. Granted, like me, my mother shares a 3.1cM segment on chromosome 2, but her match is towards the end of the chromosome, and mine is near the beginning.

Obviously I received a bit of this, and a bit of that, which in total just happened to create these small matches. After all, we both have human DNA. But it's pure chance!


The Rathlin Island Men

DNA analysis on the bones of three Early Bronze Age men, discovered in a cist burial on Rathlin Island, off the Co. Antrim coast, reveals they shared the genetic ancestors of modern-day Irish people. Their ancestors hailed from the Pontic Steppe on the northern shores of the Black Sea. It is estimated these guys lived about 4,000 years ago.

There is perhaps a greater chance of finding legitimate matching segments with the Rathlin Island crew. Such segments would be small, and match solely IF they are prevalent among the Irish population today. So...

Perhaps I do share an ancient connection with Rathlin Man 1. I have no matching segments exceeding 3cM with Rathlin Man 2 (F999802) or Rathlin Man 3 (F999801), maybe because their genomes were not sequenced to high coverage. But, I have seven matching segments exceeding 3cM with Rathlin Man 1, and the largest segment is a whole 6cM. Tiny!


But look, my 4cM matching segment on Chromosome 4 was probably passed down to me by my mother. It would take a whole lot more work to investigate this any further, so I'm just going to take it as gospel, and say I'm related to Rathlin Man 1, haha!!! 😉  None of the other segments were inherited from either of my parents, rendering them truly false matches - pure coincidences - identical by chance, once again.

What do we really learn from these tiny matching segments? We learn not to rely on such tiny segments as genealogical proof, that's what!

But, isn't it mind-blowing to think we can compare our DNA with the DNA of those who walked the shores of Ireland two and three thousand years before Christ was born.

Sources:
1. Margaret O'Brien, 'Do You Share Ancient Irish DNA? Find out with GEDmatch', 2020, Data Mining DNA.
2. Lara Cassidy, et al, 'Neolithic and Bronze Age migration to Ireland and establishment of the insular Atlantic genome', 2015, PNAS.

5 comments:

  1. I haven't done this with the test I manage. You aren't sending me down a rabbit hole, are you Dara?
    I actually came to the same conclusions as you did after viewing the tables you included. It's great that you have both your Mam's and your Dad's tests for comparisons.

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  2. It was a rabbit hole Cathy, I admit, but it didn't waste much time and it was fun! I am glad I got my parent's DNA tested, especially since I have since lost my Dad. It makes him seem closer to me, somehow.

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  4. How amazing! Thank you for writing about this. I did the tests on my father's DNA, he has 9 shared segments with Rathlin Man 1-- the largest being 6.1 at chromosome 4 and 5.7 at chromosome 18. I have significant matches at the same spots on 4 and 18 also.

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I'd love to hear your thoughts on this!