Monday, February 1, 2021

The Story of Bernadette - Part 14: Comparing Admixture Results

DNA graphic
At this point, I decided to backtrack and revisit Bernadette’s admixture at AncestryDNA. The term “admixture” is another way of saying ethnicity results based on comparing a person’s DNA to specific gene pools to determine their ethnic mixture.

Predicting ethnicity percentages is an evolving “science” and somewhat speculative. Current testing can be certain of continents (such as a person’s ancestry being 75% European and 25% African), but narrowing the percentages to specific regions is still an approximation and should be viewed as such. Results vary between testing companies due to different test populations used by each company; different parts of a genome being tested; and differences between test companies in designating ethnic regions. Taking all of this into account, a person will never see the exact same ethnicity percentages when comparing DNA test results between companies. Your comparisons should be similar, but the percentages and regional designations will always vary.

You will also see similar but differing ethnicity results between siblings even though they share the same birth parents. The ethnicity results for my two siblings are close when compared to mine, but slightly different in percentages and minor population designations.

Although I was certain after examining Bernadette’s closest DNA matches and her ethnicity results that both of her birth parents were from the same endogamous community located in Northern Italy, I thought it was worth comparing her results against another DNA cousin with the same ethnic background. I knew their results would not be exactly the same, but a close approximation in their ethnicity percentages would provide further evidence of her maternal and paternal lines originating in the same close-knit community.

I happened to manage the Ancestry results for one of Bernadette’s DNA matches (a probable paternal 3rd cousin). Since I knew for certain that his paternal and maternal sides both emigrated from the same tiny village where Bernadette’s supposed birth parents came from, he was the perfect ethnicity comparison.

I accessed the cousin’s Ancestry DNA page and clicked on the pie chart under “DNA Story”. I copied his Ethnicity Estimate and pasted it into a Word document. Next I did the same for Bernadette’s Ethnicity Estimate, pasting it in the same document below her cousin’s. The results were so similar in populations and percentages that I thought I was comparing the results of siblings instead of cousins!

Plus Ancestry includes “Additional Communities” below their ethnicity results for populations with a high concentration of similar DNA to the tester. There were three communities listed for Bernadette, all accurate for this particular endogamous ancestral group. I scanned down to her cousin’s “Additional Communities” – and yes, they were exactly the same as Bernadette’s!

I felt this ethnicity comparison was substantial evidence that both Bernadette’s father and mother were native to the same small community in Northern Italy shared by her closest DNA cousins.

Earlier I proposed the scenario that Bernadette could have been the product of a younger uncle having a relationship with another woman from their endogamous community and the baby being given to the uncle’s brother and his wife to raise. But now I was beginning to suspect the parents who raised Bernadette actually were her birth parents. For an NPE case, this was a strange turn of events!

Still, I needed positive proof of her parents’ identity and the only way to confirm their relationship with Bernadette was to find a close DNA match. This mystery may prove to be unsolvable as Bernadette and all of her immediate family members had passed away. The only test subjects left that could establish positive proof were a few descendants of Bernadette’s brother and sister.

From previous analyzes of Bernadette’s closest AncestryDNA matches, I was confident her birth father was from the same family as the descendants of her siblings. This meant a DNA test from a paternal niece or nephew would without a doubt show up in Bernadette’s results.

I had to hope a descendant would eventually test with one of the companies where Bernadette’s results were registered. If a niece or nephew did appear in Bernadette’s results, their relationship estimate would be either a full niece/nephew or a half niece/nephew, depending on whether they shared one or both grandparents (one or both of Bernadette's parents). And if Bernadette’s father had actually been her younger uncle, the DNA match would indicate a slightly more distant relationship such as first cousin, once removed.

I had much less confidence a descendant would match her birth mother as I had found no DNA matches in any of the data bases with a close association to Bernadette’s maternal lineage. It was time to be patient and wait.

DNA graphic


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