Final answer:
The statement regarding the prevalence of the O allele in indigenous populations in South America being due to the Founder's effect is true. The Founder's effect results in an increase in the frequency of certain genes within a new population that were present in the founding individuals.
Step-by-step explanation:
The statement that the O allele at the ABO blood allele locus is almost 100% in indigenous populations in South America is due to the Founder's effect is true. The Founder's effect is a type of genetic drift that occurs when a new population is established by a very small number of individuals from a larger population. This can lead to an increase in the frequency of certain genes within the new population that were present at higher frequencies in the founding individuals.
For example, the Afrikaner population in South Africa shows higher incidences of certain genetic disorders, like Fanconi anemia (FA), due to the Founder's effect; a small group of founding colonists carried these uncommon mutations, thereby influencing the genetic structure of the descendants. In the case of South American indigenous populations, if historically only a few individuals with the O allele started new populations, the prevalence of the O allele could be a consequence of the Founder's effect, making the statement true.