There are three basic types of DNA testing that those interested in genetic genealogy—the field within which genealogists employ DNA to advance their work—use. Today, I’m going to write about atDNA.
atDNA, or autosomal DNA, is what most people are interested in. It takes the DNA that we get from both parents and provides us a list of nations or regions with which our DNA matches. Notice I didn’t write “where our ancestors came from.” There’s good reason for this. It’s not like there’s a “British gene” that, if you have it, you can automatically declare your ancestors British—woo hoo!
Think of it this way. Humans (and all other organic entities, including the wooden table your computer may be sitting on) share almost all of the same DNA. All humans share about 99 percent of their DNA—yep, we are that identical. It is that one-or so-percent of differences that allow us to look, perhaps even act, different. It gives one child red hair, creates those eyes of your best friend that you envy, provides skin tone, and just about any other trait—physical and maybe, intellectual—that we see as making us different. And, that one-ish percent also reflects where our ancestors may have lived.
Around one percent does not seem like much to work with but the 23 chromosomes that make up the human genome (a genome is the complete set of genes in a living organism) contain more than 3 billion bases and 20-25,000 distinct genes. One percent of 3 billion is a lot (30 million) of chromosome bases and distinct genes (200-250) to help create those differences.
So, imagine a group of people go around the world to test populations that did not move much in the past few hundred years from their current location and then identify the parts of their DNA that differ from that of people in other regions/communities. Right now, because we don’t yet have enough information or just the right technology, how narrowly these communities can be identified for us is limited. This will not always be the case.
These differences create a British genetic signature and a Kenyan genetic signature and a Korean genetic signature and a Venezuelan genetic signature and so on, that can be identified. You are being compared to these genetic signatures of people who live in places where your ancestors were also likely to have once lived.
Unless you are Native American, there really isn’t an “American DNA” or genetic signature because—well, let’s face it—we have been the world’s first melting pot (or salad bowl, as a professor of mine used to say) for much longer than other regions of the world.
It is how your DNA matches the genetic signature of a given nation or region that identifies the most likely location(s) of your ancestors. This is how testing companies can say a person is less than one percent North African, 42 percent European Jewish, 19 percent Irish, 18 percent British, 8 percent Western European, 6 percent Scandinavian, less than one percent Iberian Peninsula and 5 percent Caucasus. Yes, those were my results from Ancestry.com. Today.
Tomorrow may be different (in fact, these assessments are not the ones I originally received from Ancestry in 2013, though they are not that different). As more and more people get their DNA tested, each testing company creates a new set of numbers based on algorithms (math equations) designed to figure out ancestry to be used for their company. If a person were to test at each of the testing firms, the chance that each set of results will come back identical is unlikely because each firm works not just with a different algorithm but with a different pool of people who took their DNA tests to compare with yours. But, there should be enough similarities to give an accurate sense of where our DNA matches groups in each nation/region.
Since mobility has only recently been a big part of our international societal fabric, if your atDNA comes back as 50 percent British, you can be confident in thinking that about half of your more recent (maybe 300 or so years, maybe more, maybe less) ancestors lived and bred in Britain for a considerable amount of time. This certainly won’t be the case for our descendants of 300 years into the future as more and more regions become heterogeneous (mixed). Though, who knows? Perhaps new regional DNA signatures will be created from these migrations.
Then, there are a few communities, like Ashkenazi Jews (my dad) who make everything about as confusing as can be. The history of the Ashkenazi is one of mobility. Starting in the Middle East, splitting then between the Caucuses (Turkey, Iran, Iraq, Syria) and those who migrated to North Africa and the Iberian Peninsula (Spain); then the group in the Caucuses primarily migrated north and east to Eastern Europe, where the majority of Ashkenazi settled beginning in the 11th century.
This mobility was primarily a response to persecution in each region forcing entire communities to move together. The fact that Ashkenazi moved with their communities for a millennium or more meant they married within their own communities and rarely with those outside it (endogamy). The genetic signature of Ashkenazi so strongly reflects endogamy that atDNA matches are difficult to define as these will be significantly higher than for those in exogamous (marrying outside a cultural group) communities.
Furthermore, as you may have noted, my Ashkenazi region is listed as “Eastern European.” That’s a very large area to be from, though some sites—including Ancestry with its new “Genetic Communities”—have narrowed it down to six nations, or nine, depending. *chuckle* Finally, to make it yet more difficult, most Jews today are Ashkenazi.
Understanding all of the above will be important for when you begin to use your DNA data to learn even more. But, hopefully you can already see that DNA isn’t enough; genealogical research must go along with the science to clarify what DNA indicates.
Where does your atDNA come from? Exactly half comes from your dad and exactly half from your mom. No matter how much you look like your father, he only gave you half of the autosomal DNA you have. We will avoid any further discussion of the science of genetics and dominant and recessive genes because, for genealogists, the key is family relationships not “Who the heck did I get these freckles from?”
So, half from mom, half from Dad. Now, it is not like mom or dad has a solid block of DNA that they pass down as an identical package to every one of their children. This is because mom got 50 percent of her DNA from her dad and 50 percent of her DNA from her mom. Same with your dad—exactly half from each of his parents. And the DNA they pass down to each of their children is randomly selected from their mixed pot. So, not a block, but a mixed bag. I like the analogy of marbles in a myriad of colors.
For child one, mom gives 50 percent of her colored marbles she received from her parents. It’s plausible (though not likely) that she gives this child only the DNA she got from her father. Possible, but again, not likely. Statistically, mom’s 50 percent will be made up of 50 percent of what she got from her father and 50 percent of what she got from her mother. Same with dad.
I will use the example of Native Americans because about two-thirds of American families believe they have a Native American ancestor. No clue why this is but it is incredibly common and equally incredibly not likely. About 10 percent (one in ten) American families actually have a Native American ancestor.
Okay, so let’s say your mom’s grandfather is supposed to be Native American and her grandmother (his wife) is British and Irish. If gramps is fully Native American, he only (pretty much) has Native American DNA to pass down so mom’s dad (this grandfather’s son) will have about 50 percent Native American DNA and about 25 percent British DNA and 25 percent Irish DNA. Let’s make mom’s mom mostly German so mom will wind up at about 50 percent German. But, what will she get from her dad who has three regions to pass down?
In almost every case, mom will wind up being nearly 50 percent German, 12.5 percent Irish, 12.5 percent British and 25 percent Native American. Yeah, it’s all about statistics.
Since each person’s DNA is akin to a bag of mixed marbles, it is (remotely) possible that while that 50 percent German is almost a given (depending upon what else Grams might carry in her DNA), mom could be anywhere from zero percent Native American to 50 percent. It is the luck of the draw what a single sperm or a single egg will carry when they meet. And, DNA does not skip a generation. If your mom got not one bit of Native American in her DNA, you will not have any in the DNA she passes on to you. You can only pass on what you received from your parents.
DNA is passed down randomly, so almost any combination is probable but, if you know anything about statistics, probability is a mathematical given. If your parents are half British/half Irish and half German/half Lithuanian, you are most likely going to be 25 percent each of British, Irish, German and Lithuanian.
If your dad is 60 percent French, 20 percent Algerian, 10 percent Spanish and 10 percent Peruvian and your mom is 50 percent Chilean, 25 percent Swedish and 25 percent Chinese, it is almost a given that you will be close to 30 percent French, 10 percent Algerian, 5 percent Spanish, 5 percent Peruvian, 25 percent Chilean, 12.5 percent Swedish and 12.5 percent Chinese (and with probably a very intriguing look about you). That’s pretty much how random statistics work.
Remember, you can only pass down to your children that DNA which was passed down to you. And, while you randomly pass down your DNA to your children, statistically, you will usually pass down nearly equal shares of what you have.
Let’s throw in a chimpanzee wrench (like that evolutionary reference? *grin*). Mom is just about 100 percent Egyptian. Let’s envision this using the marble analogy. Mom has 50 marbles to pass down that are all some shade of purple, from thistle to dark purple. Mom gives her first child 20 Purple Pizzazz, 15 Pomp and Power, and 15 Mulberry marbles. Second child comes along and he gets 30 Psychedelic Purple and 20 Purple Pizzazz. It’s all still (in this case) Egyptian DNA but it’s not always the same combination of the mixed bag of chromosomes/genes that mom got from her two parents who got their DNA from their four different parents who got it from their eight different parents.
If Dad has 20 “Scandinavian green marbles” and 20 “Russian yellow marbles” and 10 “Irish pink marbles” to pass down to his first child, he will most likely pass down 10 of the Scandinavian marbles but it probably won’t be the same exact 10 (of his 20) green marbles that he will pass down to his second child. And, if Dad also passes on 13 yellow marbles to his first child, he may pass on only 11 to his second. Again, close to predictable probabilities but not always exact.
To finish this out, most of us who work on family trees know that the number of grandparents we need to track grow exponentially with each generation.
8 great grandparents
16 2x GG
32 3x GG
64 4x GG
128 5x GG
One branch of my Helferich family tree goes back many generations but atDNA tends to cover maybe 300-400 years (on the far outside), which brings me to my 7-times great-grandfather (1653-1736). If my atDNA does, indeed, include DNA from this 7x GG, then my DNA includes DNA from many of 512 great grandparents. That, is a lot of marbles.