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How can I be closely related with someone who shares no ethnicity with me? I have multiple matches on Ancestry.com with whom I share absolutely no ethnic groups. One of these matches is at 145cM and is listed as a potential 2nd-3rd cousin. How can I share so much of the same DNA but none of the ethnicity?

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  • I have mutual matches the 145cM cousin on my mom's German paternal side (via great aunt). Ethnicity on this side of the family can be traced ancestors back 300 yrs. Ancestry.com has updated my ethnicity 6 times in 6 yrs (gaining, losing, & regaining groups) which makes me question their methods. In previous results I did have 1 common ethnicity with the 145cM match (English) 4 yrs ago. But the 145cM is a very recent match. Weirdly, now Ancestry has transferred my mom's ethnicity to my father! Before I had 75% DNA from my dad tho my parents don't shared ethnicity. Not sure how that can be.
    – user15012
    Commented Sep 5, 2022 at 16:57

2 Answers 2

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If you look at the big picture, by comparing the amount of shared cMs at The Shared cM Project, 145 cM doesn't look like "so much" DNA, compared to a very close relative like a sibling or half-sibling. Keep in mind that the DNA that gets passed down to us is randomized. Consider both the longest segment shared as well as the total cMs, and when possible, differences in generation or age between you and your matches.

Putting 145 cMs into the calculator gives this advice:

Most distant common ancestors

Assuming no pedigree collapse or endogamy, and that you're related in just one way, the furthest back you might need to go to find common ancestors for a match of 145cM is 4th-Great-Grandparent level or generation 7 on your pedigree chart. The connection may be closer.

Underneath you'll find a breakdown of the percentages for the most likely relationships, a link to the WATO (what are the odds) tools, the ability to visualize different possibilities in tree form, research guides, etc.

Ancestry provides several different "white papers" to explain how the various parts of AncestryDNA® work.

From the main article: AncestryDNA® White papers:

Ethnicity estimates

Our ethnicity white paper outlines the science behind our statistical estimation of the historical origins of your DNA. By comparing the DNA of the people in our database to the DNA of people of each region in our global reference panel, we determine the degree of similarity and create an estimate based on that analysis.

and

DNA matching

Our matching white paper describes the process by which we determine how people in our DNA database are related to one another. Using identical-by-descent analysis, we identify pairs of customers who have long segments of identical DNA that’s suggestive of a recent common ancestor. The number of these shared segments predicts the closeness of the relationship.

Ethnicity estimates are estimates, based on reference panels. Judy G. Russell has a long-running series on her blog The Legal Genealogist to remind us of that.

In short: It depends.

Different testing companies can come up with completely different ethnicities for the same person. Two siblings testing with the same company can have two very different ethnicity estimates. DNA geeks who know the different panels and chips, who can dig down into the data, might be able to glean significant clues to help with the their research, but for the casual researcher who is looking at the ethnicity estimate without understanding the underlying process that Ancestry used to generate it? It might as well be a party game.

Bear in mind, too, that someone's surname might not have any bearing on their genetic heritage. A child might bear the Italian surname of their beloved stepfather, while their birth father came from a completely different country or ethnic group. The apparent ethnicity in someone's tree might not line up with the ethnicity estimate from a DNA test for many different reasons.

Look at shared matches to get a better sense of the big picture.

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This is an example of the uncertainty that the current "admixture" algorithms have. And in some cases the same test has different results: some ppl have reported that their DNA results varied depending of the vendor's algorithm. Most of the time the DNA results seem to be far less useful for genealogy.

https://www.nbcboston.com/news/local/dna-kits-yield-different-results-from-different-genetics-companies/125109/

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