Final answer:
The high prevalence of type O blood among pureblood Native Americans is best explained by the founder effect, which is derived from genetic drift and results in a predominant allele in a population.
Step-by-step explanation:
The observation that most pureblood Native Americans have type O blood is best explained by the founder effect. The founder effect is a magnification of genetic drift in a small population that migrates away from a large parent population, carrying with it an unrepresentative set of alleles. When a small group of individuals from a larger population establishes a new population, the genetic makeup can significantly differ from the original population, leading to a predominance of certain alleles, such as the type O blood allele in this case.
Population genetics is a field that studies how selective forces, genetic drift, and gene flow change a population through changes in allele and genotype frequencies. In the early twentieth century, scientists began to recognize that these mechanisms can drastically influence the genetic makeup of a population over time. This understanding has provided explanations for particular genetic patterns observed across different human populations, including the distribution of blood types among Native Americans.