Answer:
In the ABO series, the gene for blood type O is recessive, while A and B are dominant genes, and AB is codominant.
Step-by-step explanation:
A recessive allele can be described as an allele which gets masked by a dominant allele. Hence, a person having O blood type will have the genotype OO.
A dominant allele can be described as an allele which suppresses the effect of a recessive allele. Hence, a person with A blood type can have the genotype AA or AO. A person with blood type B can have the genotype BB or BO.
The blood group AB is co-dominant. The genotype of the person might be A, B, AB or O.