The Bombay phenotype occurs because there is a mutation in t…

The Bombay phenotype occurs because there is a mutation in the gene encoding substance H, which is required for antigens A and/or B to attach to red blood cells. So, people with the Bombay mutation, even though they may have the A/B genes, do not have A/B on their red blood cells and are functionally type O (lacking A/B antigens). Which concept does the Bombay substance H gene mutation demonstrate?