Question

Explain why the two alleles, ia and ib, that produce the ab blood type are said to be codominant.

Answer 1

In codominance, both the alleles are expressed simultaneously wihout mixing of the traits. So in blood group AB, both the antigens A and B are produced. Thus it is called codominance.
see this for more info http://ghr.nlm.nih.gov/glossary=codominance

Answer 2

thank you