For codominant genes, the standard procedure of using capital and lowercase letters for the different alleles is inadequate. For codominant genes, a superscript is used. For example, the human blood type A allele is indicated as "IA" and the Type B allele is indicated as "IB." The recessive allele that is responsible for Type O blood is still given the lowercase letter "i." In a family of six children, two are blood Type O, two are blood Type AB, one is blood Type B, and another Type A. What are the possible genotypes of the parents?