Answer:
O founder's effect
Step-by-step explanation:
A founder effect can be defined as the loss of genetic variation when a new population is established from a few individuals. This process is known to increase the frequency of particular gene variants (alleles) at different loci when they are selectively neutral (or nearly neutral), and thereby such genes are fixed by genetic drift (i.e., through the random sampling of founder individuals). Interestingly, it has been discovered that the majority of South American and Central American Indians are nearly exclusively in the O blood group, which has been further associated with random genetic drift and a founder effect.