1. **Problem Statement:** Given that the ABO blood groups are determined by alleles $I^A$, $I^B$, and $i^O$, where $I^A$ and $I^B$ are codominant and dominant over $i^O$, and a mother with blood type O (genotype $ii$) has an infant with blood type O, determine the possible phenotypes of the father. 2. **Key Genetic Rules:** - Blood type O means genotype $ii$ (two recessive alleles). - Blood types A and B require at least one $I^A$ or $I^B$ allele respectively. - Codominance means if both $I^A$ and $I^B$ are present, the phenotype is AB. 3. **Analysis:** - The mother is type O, so her genotype is $ii$. - The infant is type O, so genotype must be $ii$. - The infant inherits one $i$ allele from the mother and one $i$ allele from the father. 4. **Conclusion:** - Since the infant has genotype $ii$, the father must have at least one $i$ allele to pass on. - Therefore, the father can be type O ($ii$) or type A ($I^A i$) or type B ($I^B i$), but not type AB or type A/B homozygous without $i$. 5. **Answer:** The possible phenotypes for the father are O, A, or B. Hence, the correct choice is option 5: O, A, or B.