Eli5 How does DNA testing show if someone is specifically from a certain heritage like Italian or Jewish?
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In the case of 23and me, SNPs are used. SNP stands for Single Nucleotide polymorphism. From what I can gather in a couple of searches, most companies like ancestry also use SNPs.
To get into how these SNPs work as a tool for identification, we need some background first. DNA is made out of a bunch of nucleotides, some are very important and when changed can have a large impact on genes and thus the human the DNA belongs to but most don’t. These nucleotides that do not matter can mutate and not cause issues, so can be passed on in generations. If this is a mutation in a single nucleotide causing several options or polymorphism this is a SNP.
When you know an ancestor long ago had certain mutations, all their offspring likely has at least some of these mutations. So when reading the DNA, you look for these SNP patterns. All humans are more or less related and people in a single ethnic group are generally more closely related. So if one Italians has a certain SNP, his distant cousin who is also Italian is likely to also have that SNP.
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