autosomalme | DNAeXplained – Genetic Genealogy

You’re invited to come along with me on a journey. It’s an epic event, a journey into the deepest recesses of our cells, into the smallest pieces of our DNA, into the part previously thought to be useless because it’s so tiny. It’s the journey to find minority admixture. Minority in this case means small amounts of admixture. In my personal situation, this means both Native American and African.

People who have larger amounts of admixture don’t necessarily have to do this, although it can still provide useful information. If your autosomal percentages are uniformly recognized and reported by most or all of the testing companies, meaning over 1%, you probably know which of your relatives contributed your minority heritage and you don’t need to look for that proverbial needle in a haystack. Not everyone is that fortunate. I’m not. I know of Native heritage through my mother’s Acadian ancestors, but the ones in my father’s side have consistently eluded identification. It’s there, but where? It’s haystack time for me!

This past year or two, genetic genealogy has been hallmarked by advances in autosomal DNA and the supporting technologies using tools like 23andMe and Family Tree DNA’s Family Finder tests. In order to figure out how people are related to you, what level of cousins they are, and which genealogical line they come from, we’ve been using independent tools like phasing, where you compare your DNA to that of your parents or other close known relatives to see who gave you which pieces, or segments, of DNA. Then, when someone matches you on that segment, you can tell which side of yoru family it came from, and sometimes which genealogical line it came from. This sets the stage for one day being able to have this conversation with someone:

“Hi John, I see that we are 117^th cousins and we have a match at location 17,387,426 on chromosome 3.” Beth

“Hi Beth, why yes, we are indeed cousins, but we’re actually 115^th cousins, 11 times removed instead of 117^th cousins. Our match is through Attilla the Hun’s 37^th concubine.” John

Ok, so maybe I’m dreaming a bit…but this conversation is not just a possibility, it’s a certainty 10 years from now, but perhaps with less dramatic cousinships:)

To date, the rule of thumb for finding ancestors has been that small matches should be disregarded because they are probably identical by state (IBS), not identical by descent (IBD), meaning not useful genealogically.

What’s IBS you ask? It’s a segment that is typically too small to be counted as an IBD, or identical by descent, segment. This means that you and the person you match on this small segment descend from a common population, not necessarily that you share a common ancestor within the past several generations. Genealgoically relevant segments are recognizable because they are larger. To understand why and how this works, refer to my article, “Autosomal Results, the Basics.”

There is no absolute line in the sand, but generally segments smaller than 7cM (centimorgans) or 700 SNPs (some say 5cM and 500 SNPs) fall into this category. Dr. Tim Janzen, the genealogical “father of phasing” discards all matches in his spreadsheets less than 3.5cM. That’s because he’s looking for positive genealogical matches and does not want the data to be cluttered up by possible IBS matches.

However, when you have small amounts of minority ancestry, it stands to reason that these small tidbits could be very useful in identifying which of your genealogical lines produced these small amounts of admixture. If you can identify which lines provided this minority admixture, then you’re well on the way to identifying which ancestor contributed the minority admixture.

When looking for minority admixture in two related people, finding these small segments in the same location should provide meaningful information and confirm minority heritage. Said another way, if you both have less than 1% Native heritage, both share a common ancestor, and both carry your less than 1% on the same segment….one might say it’s not likely to be coincidence, especially if there is a pattern across multiple chromosomes/segments. Identifying the common segments of your common ancestor can lead to identifying the specific family line, especially if you match others as well. In essence, this is the genetic equivalent of “surround and conquer.”

Let me give a very short example here.

Let’s say I match my mother on part of chromosome 1 that is Native.

Then let’s say I match her first cousin (my first cousin once removed) on mother’s mother’s side on a smaller piece of that same segment. This immediately tells me that this particular bit of Native heritage is not from mother’s father’s side.

Another match to a more distant Hill cousin further defines the path of Native ancestry, showing that the Native heritage came through mother’s grandfather’s mother’s line. You can see how we track this ancestry and whittle down the possible sources.

So, I’ve set out to test this minority ancestry tracking theory. Because we are dealing with such small segments of DNA, “rooting around in the weeds,” as Bennett Greenspan so aptly put it, and have no mechanized tools, this journey is long, tiresome and tedious. It’s also thrilling.

As with all experiments, I have wondered many times if I was wasting my time. I’ve completed steps and then redone them a different way when I realized there was a better or more revealing method. More than once. That comes with the territory.

I debated about how to share this new technique. In the past, I would have published this as an academic paper, but with the delays surrounding the publication of JoGG, and the fact that the last paper through JoGG took 18 months to get out the door, much of this information would be stale by then. I thought about publishing as an e-book as well, but I finally settled on my blog. I feel that I can reach more people in a much more timely fashion this way. I also really like the blog because I can write in a more relaxed fashion than I could in any other venue and it gives you the opportunity to interact as well.

I also don’t know what to call this new methodology. I have just been referring to it as the weeds method, but that’s not very scientific. I considered the APM technique – Ancestry Population Mapping. Sounds too nonspecific. The PTM – Personal Torture Method – nah – puts people off even if it is true. MAT – Minority Ancestry Tracking – that’s a possibility but isn’t very specific. Fragmented Chromosome Mapping, FCM, has possibilities. So, I’m open to suggestions. If at the end of this series, it’s still the weeds method….well, then weeds it is.

Over the next few weeks, I’ll be writing about this journey, my discoveries, and sharing techniques with step by step instructions so that you can use the same tools. Join me for the multi-part series, “The Autosomal Me.”

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