how do dna testing companies calculate the percentages of your origin and how can they be so exact?
In: 15
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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