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.
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.
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