The Bureau of Indian Affairs has used a "blood quantum" definition of generally, one-fourth degree of American Indian "blood" and/or tribal membership to recognize a person as an American Indian. However, each tribe has a particular set of requirements, typically including a blood quantum, for membership (enrollment) in the tribe. Requirements vary widely from tribe to tribe: a few tribes require at least a one-half Indian (or tribal) blood quantum; many others require a one-fourth blood quantum; still others, generally in California and Oklahoma, require a one-eighth, one-sixteenth, or one-thirty-second blood quantum; and some tribes have no minimum blood quantum requirement at all but require an explicitly documented tribal lineage.
To learn about Tribal Nation Citzenship and Blood Quantum requirements see the following website:
Chickasaw Nation Citizenship
Muscogee (Creek) Nation Citizenship http://www.muscogeenation-nsn.gov/citizenship/cit%20criteria.htm
Choctaw Nation Citizenship http://www.rootsweb.com/~itchocta/apps/apps_cards.htm
Cherokee Nation Citizenship
Seminole Nation Citizenship http://www.seminolenation.com/admi_enro.htm