In three cities of Chile (Santiago. Valparaiso. Valdivia) the A allele and phenotype (ABO blood group) are more frequent in the higher socioeconomic strata (SES) and the O allele and phenotype are in the lower ones. This constitutes a structured sociogenetic cline (SGC). https://www.bekindtopets.com/save-now-Aqua-Pure-3MFF101-Full-Flow-Drinking-Water-System-Replacement-Cartridge-flash-choice/