If a blood donor has genotype hh, AB, what is his red blood cell phenotype?

The blood donor's genotype hh indicates that they possess the Bombay phenotype. Individuals with this genotype lack the H antigen, which is necessary for the expression of A and B antigens on the surface of red blood cells. The presence of A and B alleles (AB) suggests that, under normal circumstances, the individual would express these antigens.

However, because the individual is hh, they do not produce functional H antigens, which are precursors for the A and B antigens. As a result, despite carrying the alleles for A and B phenotypes, their red blood cell phenotype presents as O. The O phenotype is defined by the absence of both A and B antigens on the red blood cells.

Therefore, even though the genotype indicates the potential for A and B antigens, the lack of the H antigen due to the hh genotype leads to a phenotype classified as O.