Final answer:
No, Robert, who has type O blood, cannot be the biological father of Bobby, who has type AB blood, because type O individuals cannot provide the necessary A or B alleles for type AB blood.
Step-by-step explanation:
If Robert has type O blood (genotype ii) and Bobby has type AB blood (genotype IAIB), Robert cannot be Bobby's biological father. This is because a person with type O blood has two recessive alleles (ii) and does not have the A or B antigen. Meanwhile, a person with type AB blood has a dominant A allele (IA) and a dominant B allele (IB), which they must have inherited from each parent.
For Bobby to have type AB blood, one of his parents must contribute the IA allele and the other the IB allele. Since Robert has the genotype ii, he cannot provide either of these alleles. A person with type AB blood can only have children with types A, B, or AB if their partner also has one of the dominant alleles (IA or IB).
Blood type compatibility for reproduction must follow the principles of genetics, specifically relating to the dominance and recessiveness of alleles. If a child's blood type is such that it cannot be produced from the combination of parents' genotypes, paternity or maternity can be questioned. In this case, an individual with blood type O (ii) cannot have a child with blood type AB (IAIB). Bobby's parents must both have at least one dominant I allele (IA or IB) to produce the AB phenotype.