I understand it matches DNA from their database, and helps you meet your blood relative, but for it to be completely accurate wouldn’t every person have to use the kit for the data to be up to date?
Also, how do people have varying percentages of nationalities? Shouldn’t DNA % be a fraction of 2 because it goes like 1/2 then 1/4th, 1/8th and so on (because we have 2 sets of biological parents)
In: Biology
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I may be wrong, so don’t take this 100%, but I believe it’s 2 parts; 1 being DNA that they have from people using their kits, and 2 being legal records. So if your cousin did a DNA kit, it would show you you’re related to this person as a cousin, and the records of births, etc also show this is his dad, so your uncle, etc. That would, of course, leave room for inaccuracies considering lots of people who aren’t dads are recorded as dads, and things like that.
I’m terrible at math, so this may not even make sense, or be accurate, or answer your question, but when you go 8 generations back, a single person accounts for only 0.00390625% of your DNA, and you have 256 direct (great, great, great, etc) grandparents at that point. Let’s say 40 of those ancestors are Irish, 40 x 0.00390625 = 0.15625, so you’re 15.6% Irish. Then 37 German, 14.5%. 72 English, 28.1%. 12 Chinese, 4.7%. 53 Russian, 20.7%. And 42 Phillipino, 16.4%. If everyone reproduced in nice matching even numbers, 1 Irish for 1 Irish anywhere along the line, then I think you could always expect a fraction of 2, but considering that goes back a LONG way, and 8 generations is that tiny percentage, depending how far back you go, you could get virtually any percentages. Plus I’m sure they round them rather than listing 20.703125%, they’ll simplify that to 20.7%, so it’s not actually exactly precise.
So they have this list of spots on DNA where it’s common for people to have different values, they call them SNPs. They then make chips with chunks of ASO that match up to the DNA for these SNPs and record what is the specific mutation on that SNP that you have. To run a DNA test, they make lots of DNA copies, chop it up into little bits and put it on the chip, the chip’s ASO sticks to the DNA chucks that match the SNP, and it can tell what the mutation is for the DNA that stuck to it.
Anyways, ancestry.com has a chip that measures ~380,000 SNPs, this would technically be capable of differentiating between 2^380000 different people (way way more than the number of people on the planet).
For health info they can look up the SNPs and see if there are studies on them (often there are, in fact ancestry picked the SNPs based on if people think they are medically relevant).
For relationship stuff, they just see how many you have in common with other people, more in common means more closely related, and roughly the percentage in common is equal to your relationship distance (for the ones that are roughly 50% common).
For telling the countries for your ancestory they they test a bunch of people who say they are 100% from county XYZ (because they can name every grandparents birthplace and they are all close and in that country). Then they find the SNPs that they have in common but people in other countries don’t have and give those SNPs a score/weight for that county. So then they look at how the scores add up for those SNPs on your DNA
As you get more people in the database, the probability of getting any sort of match – showing some relationship – increases exponentially (actually its more of a logistic curve, but at first it looks exponential-like)
So people from the same village back in say scotland had more shared blood than average, so you get a relationship there. Some distant cousin already sent his kit. A bit more. People from an area have a preponderance of a couple specific types of gene – so it raises the odds your family came from there.
Eventually as people send stuff to these databases their knowledge becomes overwhelmingly wide and far-reaching.
And then they sell this information.
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