From a genetic perspective, what type of alleles would allow a child to display a Type A blood phenotype?

To display a Type A blood phenotype, a child must inherit at least one A allele. The ABO blood group system operates based on the presence of specific antigens on the surface of red blood cells. The three primary alleles involved are A, B, and O.

The A allele encodes for the presence of A antigens, while the B allele encodes for B antigens, and the O allele does not produce any antigens. A child can inherit two copies of the A allele (A/A), confirming an A phenotype. Alternatively, if the child inherits one A allele and one O allele (A/O), the presence of the A allele is sufficient to result in the Type A blood phenotype.

The other combinations provided—B/B, O/O, and A/A—do not lead to Type A blood when assessed individually or in pairs. The B alleles would lead to a Type B phenotype rather than Type A, and the O/O combination does not provide any A antigens necessary for the Type A designation. Therefore, the pairing of A and O allows for the expression of Type A blood due to the dominance of the A allele.