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Old 10 November 2017, 02:21 AM
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Icon07 Why determining ancestry is rarely accurate

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These siblings took DNA tests and got different results. Why determining ancestry is rarely accurate.

http://www.philly.com/philly/health/...-20171012.html

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“It’s very difficult to accurately find your ancestry under any circumstances,” said Jonathan Marks, an anthropology professor at the University of North Carolina at Charlotte. “There has been genetic mixing for thousands of years. These tests are fun but rarely accurate — 10 percent Scandinavian could be no Scandinavian because the test could very easily be 10 or 15 percent off.”

The imprecisions are not limited to Ancestry. My sister’s son took a DNA test from 23andMe, another popular DNA testing company. His father is Italian and Irish, named Rettaliata. The test showed no Greek and just 1 percent Italian.
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  #2  
Old 10 November 2017, 05:26 AM
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My mother had her ancestry tested from one of those sites. For $50 bucks, it told her roughly the same thing that she already knew based off of family history: she's Irish and British.
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Old 10 November 2017, 05:54 AM
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The ones I've seen will say something like "2% Sub-Saharan African". While it's nice to know that people in my (entirely Western European) family share some genes with some people in Sub-Saharan Africa, I knew that % claim was bunk right away. And not because I think it's impossible we have some distant ancestor from Africa.

First, if we go back only a few thousand years - long long after people first spread out into the world - we all have African, and European and even Polynesian, genes. People mixed at the edges a lot more than we might imagine and the genes did spread. Second, Sub-Saharan Africa has more genetic diversity than the whole rest of the planet put together. I don't believe for one second that the folks over at whatever-and-me-gene-counters have any reliable way of telling what's from there and what's not. Yet they presented it as if it's a likely fact - the rest of the nonsense as well. It was sad to see people who should know better take it as if it has a good scientific basis.

I, too, noticed a difference in siblings that couldn't possibly exist. (Between two maybe could be a random chance but between three or more?? No, I don't think we won the mixed-up genome lottery of more than one in a trillion).

They found distant cousins and so forth. Well, so? We probably have far far far more in common with our next-door neighbours than these people we've never even met.
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Old 10 November 2017, 02:12 PM
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Two friends (a brother & sister) had this done. The results came back more or less as expected for immediate ancestry, but the proportions were different. That actually made sense to me, because there are genetic differences between siblings.

Seaboe
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Old 10 November 2017, 04:20 PM
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I'm extremely skeptical of the premise. What are these Irish or sub-Saharan African genes? How do we know that's where they're from? Any given genetic trait can evolve independently in multiple locations through random mutation and, if it's advantageous in the local environment, proliferate. Of course if you study the genetic profiles of groups of people in different geographical areas you'll see trends, but someone could still end up with a gene that's common in Ireland without having Irish ancestry.

One small part of my job involves asking my clients whether they have any Native American heritage. This is to comply with the Indian Child Welfare Act, which gives tribes the right to participate in juvenile dependency proceedings or request the case be transferred to the tribal court if the subject child qualifies for membership. I've been surprised by how many of my clients have already shelled out for one of these tests, or are eager to do so. I understand they're pretty expensive, and in any case, getting a result that you have Native American heritage doesn't mean your child is eligible for membership in a tribe. But in any event, I've yet to meet someone who took one of those tests and didn't get a positive result for Native American.

ETA: My inner conspiracy theorist worries these companies are really in the business of creating a DNA database they can sell or rent to the highest bidder, whether that be a totalitarian government, health insurance companies looking to exclude high-risk patients, or some other sinister as yet unforeseen commercial enterprise. Possibly involving clones. Evil ones, perhaps.
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Old 10 November 2017, 04:27 PM
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Well, I didn't take one, but my brother did -- no Native-American ancestry reported. No sub-Sahran African, either. 100% European, 80 or 90% Northern/Western European, IIRC.
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Old 10 November 2017, 04:34 PM
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I think it was in Patton Oswalt's new comedy special, he was talking about a certain percentage that was mid-eastern and when he called he was told that was because of Genghis Khan... because he was a...prolific... womanizer.

I think it's a good reminder that interpreting DNA is more of an art than a science, and that it should be taken with a grain of salt.
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Old 10 November 2017, 04:41 PM
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Quote:
Originally Posted by Esprise Me View Post
I'm extremely skeptical of the premise. What are these Irish or sub-Saharan African genes? How do we know that's where they're from? Any given genetic trait can evolve independently in multiple locations through random mutation and, if it's advantageous in the local environment, proliferate. Of course if you study the genetic profiles of groups of people in different geographical areas you'll see trends, but someone could still end up with a gene that's common in Ireland without having Irish ancestry.
Generally, you won't find the exact same mutation arise independently in two completely isolated populations: the Sherpa people of the Himalayas, the people of the Ethiopian Highlands, and the Inca and related peoples of South America all have mutations that give them advantages for living at high altitudes, but while the effect was the same (increased oxygen transport ability) but the mutations that caused it are different in each group.

The big issue is, as Ganzfield already said, they're looking at current populations and assuming that their genetics haven't changed in the last 500 or 1000 years, when we know that humans like to get around in both senses of the term.
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Old 10 November 2017, 06:33 PM
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Quote:
Originally Posted by Esprise Me View Post
But in any event, I've yet to meet someone who took one of those tests and didn't get a positive result for Native American.
My parents both did DNA testing, but with two different companies. My dad's came back with Native American, my mother's not. It could be interesting if I were to do testing with both companies and see if there's any similarity.
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Old 04 February 2019, 07:02 AM
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I got one of these for Christmas, since apparently I'm hard to shop for, and just got it back. Yes it means they're going to sell my clones to the military industrial complex, and show me genetically specific pop-up ads, but whatever.

Quote:
Originally Posted by Esprise Me View Post
I've been surprised by how many of my clients have already shelled out for one of these tests, or are eager to do so. I understand they're pretty expensive, and in any case, getting a result that you have Native American heritage doesn't mean your child is eligible for membership in a tribe. But in any event, I've yet to meet someone who took one of those tests and didn't get a positive result for Native American.
The further back you go, your ancestors grow exponentially, so it's plausible that lots of Americans really do have trace amount of Native American ancestry. But count me as someone who didn't. I got 0% Native American. 98% European and 2% Middle Eastern. Which is mildly surprising, since the branch of my family that I have the most complete information on came to the US in the 1600s from Wales, and some lived in early Caribbean colonies. That's 10+ generations, which could mean hundreds of ancestors in the Americas. It seems very likely that some of them could have been black or Native American in all that time, but apparently not.

The bulk of my ancestry was entirely unsurprising. 75% Irish, Welsh, or Scottish. However the smaller components were not what I would have guessed, or easily explained. I got around 1/8 Scandinavian, and 1/8 various Mediterranean, which is almost exactly a full great grandparent each, but I can't reconcile either with any of my great grandparents. And the other surprise is 0% French. One of my great great grandparents was supposed to be French by way of Louisiana. Maybe she was just culturally French. Or someone passed on incorrect information about her history or someone's parentage. Or it's just the margin of error and the test is not good at figuring out ethnicity.

Regardless of how accurate it may be with these sorts of things, it did correctly identify that I was 4% related to a second cousin, and 26% related to my uncle. So it can at least do that much.
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Old 10 November 2017, 04:51 PM
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Quote:
Originally Posted by Seaboe Muffinchucker View Post
Two friends (a brother & sister) had this done. The results came back more or less as expected for immediate ancestry, but the proportions were different. That actually made sense to me, because there are genetic differences between siblings.
No, sorry, that does not make sense. If the difference were noticeable on these markers in two people in the same generation with the same parents then the difference over four or five or whatever generations they are supposedly counting back would be too great to have the test at all. Once (g)you go through that exercise you realize they aren't really making any specific time frame, that means that they aren't talking about any specific places either because that's the whole point - genes moving from place to place between population during some time. If that time frame is too small then there simply isn't enough time for the genes to move at all. If it's too large then we all have the same sets of ancestors.

So what the test really means is that (g)you share some very specific genes with people in some other place now. By choosing which genes are used as markers, that percentage could say anything for anywhere because we share more than 99% of our genome with every other person on the planet. One might as well have a test to show which mole locations one shares in common with people from Ethiopia and call that a percent.
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  #12  
Old 13 November 2017, 08:56 PM
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Quote:
Originally Posted by Seaboe Muffinchucker View Post
Two friends (a brother & sister) had this done. The results came back more or less as expected for immediate ancestry, but the proportions were different. That actually made sense to me, because there are genetic differences between siblings.
I think you're referring to my husband and his sister, or at least the facts match. The strange thing is that their father's genealogy is 100% Sicilian; their mother's is 100% Welsh. The siblings look (to the untrained eye) absolutely dissimilar. He looks very much like their Welsh grandfather. She looks very much like their Sicilian grandmother. His percentage of Sicilian DNA is much higher than hers; her percentage of Welsh DNA is much higher than his. Go figure.

And as I was the one that bought the Ancestry kits and had them do the testing, I should add: I got the kits to assist in researching their family trees, not to figure out their "country of origin" as it were. If you have a tree on Ancestry, and match your DNA kit to your name in that tree, they show your DNA matches -- people who are likely to be related to you based on their DNA, and if those individuals also have an Ancestry tree it can help your genealogical research. In my husband's family, I was hoping it would get me past some roadblocks (one ancestress was abandoned as an infant on the church steps, for example -- family legend is that she was the illegitimate child of some local nobleman, of course), but while they are getting matches, it looks like most of those people have experienced the same roadblocks. I, on the other hand, was able to confirm one branch of my tree that I was pretty sure was correct, but that I could not prove with the documents available to me.

Last edited by Tootsie Plunkette; 13 November 2017 at 09:05 PM.
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