# how do dna testing companies calculate the percentages of your origin and how can they be so exact?

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how do dna testing companies calculate the percentages of your origin and how can they be so exact?

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They look for specific marker genes that are more common in specific regions. Mutations that happened in one population and are only present in those with a heritage from there.

What do you mean by exact? Genes are always random. It could easily be that you have ancestors in some place but none of their genes got passed on (but your siblings could have them for example). The more genes you look at the more unlikely a complete lack would become though. Each generation 50% of the genes are randomly selected from each parent.

They just guess. The percentage figures are effectively meaningless but people love the impression of truth when they are spending money.

DNA testing is for fun and a few interesting conversations. In the scheme of things it means nothing because lines drawn on a map (that change with every war/conquest) are not respected by genetic transmission.

DNA testing companies do not have a “pure sample” of any “origin”. All they have are a sample from the population TODAY. Trying to work backwards to some inference is purely a mathematical game at that point – fraught with assumptions, best guesses and correlations. None, zero, naught, nil of these methods are deterministic. The best they get is that “a lot of people who call themselves A have some of this and some of that and maybe we’ll call this a marker for A”. Then as more and more samples are collected, the weaker and weaker these correlations become.

It is a guessing game based on statistics, nothing more. And one thing that everyone needs to understand with statistics – it is IMPOSSIBLE to derive a particular individual characteristic from a population statistic. The simplest example is to flip a coin for heads and tails – in the long term there is a 50/50 statistical outcome but there are ZERO coins with a side of 50/50 heads-tails, a side with either be 100% heads or 100% tails.

Omg I thought they actually collected gene samples from people in the cemetery’s from 300-400 years ago to say that that’s where they came from….

This doesn’t answer your question, but I’d be very wary of providing one of these companies with my DNA.

They calculate them by comparing your DNA to everyone in their database.

In other words, it’s not “so exact”. It’s not even close. Give your DNA to four different companies and you’ll get four different results as far as percentages go, because they each have their own database.

The answer is, they are not accurate. If you read the fine print, they tell you that this is just for entertainment and has no actual meaning. But basically it’s just a guess made based on certain markers. But it’s in no way accurate and these companies make no such claim, as far as I am aware.