Blood quantum is not about blood. At no point does blood get involved in the system of sequestering indigenous people. There is never a blood draw. One can be told from analyzing cheek cells which groups one might belong to, but the people who are designated indigenous are reluctant to let a real data base be built, because genomic info might be used by pharma countries to create new meds which make a lot of money. None will go to the donors.
Money is the key. NOT blood. The first lists of indigenous tribes were made before anyone even knew about the basic blood groups of A, B, and O, much less understood a genome. But indigenous people have been kept from making money or even profiting from their land. Therefore money will motivate them to rage to be "in" and fight like hell to keep as many as possible "out."
This whole "blood" thing comes from British domestic animal raising in which keeping one group of animals together and other groups out has caused genetic drift to define Hereford cows from Hereford, England, and Dorset sheep from Dorset, England. No indigenous people are from Europe, by definition. Their self-definition as a group was partly hereditary and partly by affinity, folks who just fit in kinda by accident.
When the scientists were pressed to define species, this is what they said.
"A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial, e.g., Homo sapiens."
That is obsolete. First, we discover there are many if not the majority of "similar individuals -- THERE's a punt! -- that can exchange genes the old-fashioned way, sex as meiosis. ("Hey, you big strong Neanderthal!) But vectors can move genes from one person into another, so why not into a dog? A virus is a bit of nuclear code without a cell. If it will fit into the nuclear code, it can become an inheritable part.
An accusation has been made that when modern people have to send in their blood for analysis for sports competition, they sometimes send dog blood -- since all it is tested for is whether there are drugs in it. I would not be surprised by dog genes in humans, nor would I be surprised by drugs in either. I impounded a dog in Portland that had every symptom of barbituate poisoning. There was a drug house with a golden retriever that was sometimes too mellow to do anything but wag its tail and other times offered to tear out my throat.
The "principal natural taxonomic unit" is what you call it. If you call it a dog, it's a dog. But now our prob is what is a Neanderthal? Do we call it a human? Even today there are some people who cannot bring themselves to call an autochthonous person a human. They say "vermin," "animals". They repeat "nits make lice," and are surprised by people remembering.
Back to blood. Even after raping their slaves and producing children, whites believed they were the only human species and prevented with law any marriage between them and anyone not like them. To get married, people must still get a blood test. Chart at https://www.nolo.com/legal-encyclopedia/chart-state-marriage-license-blood-29019.html They test mostly for diseases and hurtful mutations. Easy to defy the law: don't get married. Slaveowners didn't.
There are two ways that there is a division about marriage -- not sex. One is being two different species, so you're not allowed to marry your beloved dog or pony. Never fear, you can go ahead to create a legal document like a marriage agreement about your relationship. Best not mention sex. This might or might not be accepted by one's religion.
The other chasm is about culture. People of different cultures are advised not to marry. It happens anyway, esp. in wartime or if there is an overriding and inclusive culture like shared work or even intense experiences. But it's highly romantic and the work can be worth it. The line between who is on the tribal rolls versus who is not is complicated by the role of marriage. Being married does not guarantee blood relationship via sex. Culture is not determined by blood. It just teaches you what you think you know about blood.
Your genome cannot be determined by your blood because blood cells have no nuclei, which is where the genome dwells. Cheek cells carry your genome, but no one says "cheek scrape quantum." Your genome CAN determine whether one has an Asiatic basic genome structure, since it is confirmed that before Columbus the indigenous somehow got across the Pacific Ocean. (It was NOT immigration.) European, African, and Asian genomes are different enough to sort because they have been separate for so long, mostly. But American difference goes back a long time.
Determining tribe would not be practical. Different eating patterns, different local mineral isotopes, individually mutated genes like the capacity to dive deep and stay down long, would need far more lab work than the pop commercial genome spit tests. None of that could have been done at the time of identifying "tribes." They simply set up a table and made a list of everyone there who said they belonged. There were no objective criteria. By the time they got to the prairies, even adaptable white people had become tribal members. Since they were defined by culture, they WERE members.
Some were split -- white with their back-home families and tribal with their new native families, some of whom were biologically and literally blood quantum relatives. (Custer, like many, had two wives: one indigenous and the other white.) Being on the list meant food -- this was a military operation by the Department of War, not a mission, though they also kept records.
The most insidious assumption had the culture cleavage down the middle of it. Tribal people accepted being defined by the Other. There was a bit of Stockholm Syndrome -- by golly, if being like these white people could be defined as success, they were up for it. After all, the cavalry would shoot you if you were too out of line. But if you were compliant, you ate.
But the whites were assuming that after the first few generations when the People would naturally try to get their children and grandchildren on the list -- they were probably still culturally indigenous or partly so -- and then they would settle down, by then diluted into sorta white anyway. But they didn't. The dilution was cultural and the white culture was changing as well. Then the indigenous people to the south started coming north. Egads!
"The U.S. will become “minority white” in 2045, Census projects". Yikes! What if they remember what we did to them? What if they demand their land back? I'm on Twitter with a lot of Western Canadian indigenous people. "What if" is here. So "What now?" It has nothing to do with blood. It's about culture.