Answer:
A - AA/AO
B - BB/BO
O - OO
AB - AB
Explanation:
An individual inherits their blood type from their parents like it inherits many other traits. However, there's something interesting about this.
Blood type O is always recessive, which means that an individual needs to get a copy of the O allele from both of its parents in order to have the blood type O (genotype OO).
Blood types A and B are codominant to each other, which means that the effect of both A and B alleles is expressed if an individual receives them. If an individual receives the A allele from one parent and the B allele from the other, it will have the AB blood type (genotype AB).
Blood types A and B are both dominant to the O allele. This means that an individual can have blood type A or B either by inheriting two copies of the A or B allele or by inheriting one copy of the A or B allele and one copy of the O allele (genotypes AA/AO and BB/BO).
You can take a look at the image below to understand this more easily:
