In the ABO series, the gene for blood type O is, while A and B are genes, and AB is.

Gene for blood type O is recessive

Gene for blood type A and B is dominant

Gene for blood type AB is neither dominant nor recessive but a form of co-dominance

Explanation:

In the ABO blood group,

A and B are dominant genes, O is recessive genes.

So the different genotype and its corresponding phenotype is as follows -

Genotype Phenotype

AO A

BO B

AB AB

AA A

BB B

OO O

Hence, the two alleles AB occur and express together. Therefore, AB blood group is an example of co-dominance.

Blood type also varies with the presence of Rh factor. If Rh factor is present, the blood type will represented with a "+" symbol. And if Rh factor is absent, the blood type will be represented by "-"symbol.