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
In North America, you a certain percentage of your ethnicity must be Native American in order to qualify for recognition by the government to receive tribal benefits. I think it's a minimum of 1/12th. in the US (not 100% positive on the exact number). This is called the "blood quantum."
If you don't meet the minimum, regardless of how or where you were raised, or what you look like, or what languages you speak, you are automatically disqualified from stuff like scholarships, reparations, and official membership to a federally recognized tribe. This was put in place in the early 1900s by white people with no discussion about how Native Americans establish heritage or tribal membership.
A lot of racism in the US still lingers around this concept where a person is or isn't part of an ethnicity based on their blood quantum, rather than their lived experiences. Someone who is 1/4th. black, for example, may have their concerns dismissed because "they're not really black." That is until it becomes convenient for the racist to go by the "one drop rule," which is when a person has any non-white heritage, they are no longer considered white (even if it's something like 1/100th. black).
Depends on the tribe/nation, which is the insidious part of blood quantum. It's a genocidal tool developed by settlers but implemented and enforced by comprador governments themselves.