Spit in a tube and we’ll tell you where you come from: that’s the basic premise being offered up by DNA ancestry kits, which have soared in popularity for those who are curious – or who’ve run out of Christmas present ideas.
We’ve all heard of the horror stories of people using the kits and finding out they’ve dated their long-lost cousin. Of course, they don’t mention that in the adverts – but what’s the reality behind the main feature they market themselves on? Can one of these tests really tell you if your ancestry is n percent Irish, West African, or South Asian?
The way DNA testing companies begin to calculate ancestry percentages is by comparing thousands of tiny sections of your DNA that often vary between people, known as single nucleotide polymorphisms or SNPs. If we talk about it in terms of those four letters on every high school biology test, in a spot of DNA where you might have a letter “A”, someone else might have a “C”.
These points of variation are compared to those of people in reference groups, made up of those meant to have “known” ancestries – their families have lived in the same place for many (exact figures seem to be unspecified to the consumer) generations.
Well, we say comparing; what they actually do is look at the particular SNP you have, and then look at how often that same variation pops up in the various reference groups representing particular regions. If, for example, it shows up 80 percent of the time in the France group, but only 5 percent in the Russia group, then that part of your DNA will be tagged as most likely “coming” from France.
That’s done with each of the hundreds of thousands of SNPs used as markers and tallied up. So, when you get an overall result that reads, say, “42 percent – Spain”, what it means is that 42 percent of those particular markers also pop up a decent chunk of the time in a group of people with “known” ancestry in that area.
Thing is, the term “known” can be applied only loosely to these reference groups. First, companies aren’t the clearest about how they determine reference group criteria; is ancestry self-reported, or do people have to dish up official records? Any scientist worth their salt will tell you that self-reported data isn’t always the most reliable (although, funnily enough, DNA testing can also cast doubt on the reliability of official records).
Even if it were reliable, that doesn’t mean the people in reference groups have inherited the same variations as their ancestors had. That’s because we inherit DNA in two halves, so you’re not guaranteed to get a particular chunk of it.
“You start with two parents, then four grandparents, then eight great-grandparents, it goes to 16, 32 and so on. And by the time you go 10 generations back, there are ancestors from whom you inherit no DNA,” explained geneticist Professor Mark Thomas to The Guardian.
Then there’s the matter of how many people are in each reference group – some regions might be better represented than others, so without all the possible data, you’re not necessarily getting the fullest picture.
Of course, more people might be added over time and that’s excellent news for representation – but it also means that your percentages might change over time as the data does, which, if the information above hasn’t already, somewhat shatters the illusion that these tests tell you something deep and meaningful about yourself.
Bottom line – these tests are fun, sure, but maybe take the results with a pinch of salt. After all, DNA isn’t all that we were, are, or will be.
All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.
Source Link: Asked For A DNA Genealogy Kit For Christmas? Here’s What They Actually Tell You
