After 32 generations (~800 years) you have more genealogical ancestors than there are base pairs in human DNA. There literally isn’t enough resolution to store a “record” of each of your ancestors, even if you inherited exactly 1 base pair from each ancestor.
Additional complications make it an even shorter timeline. After about 8 generations, you share no more DNA with your ancestors than you do with a random stranger.
Politically this should be more well known. Of course, racists and fascists rely on “blood quantum” arguments to justify racial or ethnic oppression. But they don’t invent this idea of strict genetic identity. It’s latent in the population.
Leftists should more frequently call out genetic tests like 23andMe as inherently racist because it’s based in race science nonsense. It may not be as obvious as Nazis invoking aryan genes or whatever; but it’s still just as incorrect when your aunt at Thanksgiving talks about how she discovered she’s 2% Choctaw or whatever
Not an expert but
In the first place, mitochondrial dna are shared among many people, for the basic fact that it is passed matrilineally. This allows us to prove the existence of the so-called Mitochondrial Eve, to whom all humans alive today are related.
Second, the mitochondrial dna encodes basically the production of ATP. Not genes that would be used to express any apparent difference between people.
Third, the number of base pairs in mitochondrial dna is very small, tens of thousands, compared to the 3.1 billion base pairs in nuclear dna.