In New Mexico, some pueblo Indian tribes - such as Isleta - have started to enforce the 1/2 blood quantum for people to maintain membership on the tribal roll. One of the factors instigating this strictness is the distribution of casino profits to tribe members (the rule came up just as $2000 checks were being cut for each member of the tribe). The more members; the less $$ per person. This means that some long-time residents of the pueblo are losing their membership and such benefits. Some of those being kicked out are ones who married into the tribe (even if their kids qualify) and those originally from other tribes who live there and participate in pueblo life. Apparently there are a few Navajo families living at Isleta who have been there for generations and even have a religious kiva there.
Here is my thought: what if a full-blooded Isleta man were to sell his sperm for artificial insemination to a non-Indian woman so that her children could qualify for casino profits and have other benefits of tribal membership? These children could prove 1/2 Isleta blood, even if they have never set foot on Indian land.
Other tribes worry about using blood quantum as opposed to decendency records for tribal rolls because there are so few members with enough blood, that they will necessarily become more diluted as they marry outside the tribe and eventually the tribe might cease to exist. Again, if a man with at least 1/2 blood quantum in this tribe were to offer his sperm for donated insemination to a number of women, the tribal roll could be increased amply. The problem here would be that these children would be half-siblings and so could not marry.
Anyway, I see a for-profit Native Donor Insemination Business opportunity here for somebody.