In humans, blood groups are produced by combinations of three alleles $I^A$, $I^B$ and $i$ - HSC - SSCE Biology - Question 17 - 2023 - Paper 1

To determine the possible genotypes of the father, we recognize that the mother has blood type O, which corresponds to genotype $ii$. Since the child has blood type A, the child must inherit an $I^A$ allele from the father. Thus the father must either have genotype $I^A I^i$ (having one $I^A$ and one $i$ allele) or genotype $I^A I^A$ (having two $I^A$ alleles). Therefore, the correct answer that includes all possible genotypes of the father is option C:

C. $I^A I^i$ or $I^A I^B$.