What would be the blood type of a person who inherited an allele from one parent and an allele from the other?

Codominance means that neither allele can mask the expression of the other allele. An example in humans would be the ABO blood group, where alleles A and alleles B are both expressed. So if an individual inherits allele A from their mother and allele B from their father, they have blood type AB. I hope it helps!