Eli5 How does DNA testing show if someone is specifically from a certain heritage like Italian or Jewish?
In: 5
When DNA mutates that change is mostly permanent. A protein in a certain section changes from one type to another. When that person procreates and their children procreate, the mutation spreads in the population. In old times, when travel was less common, it allowed a group to have a higher than normal prevalence for a particular mutation.
Now, companies like Ancestry.com take the DNA from millions of people and match it up with family tree and personal data from all of them to show that people with a certain gene expression linked to freckles have family histories in Ireland, including families that never left Ireland.
So, if you have that particular gene expression, you will get recorded as being partly from that region.
There are an astronomical number of gene variations, and the more of them they can match up, the more confident they are as to where your family came from and what groups they didn’t come from.
My DNA marked me as being from a small county in Poland, and had no markers for Jewish ancestry, meaning I am Eastern European (in part) but not Jewish.
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