Which of the following accurately describes the patterns of inheritance in human blood types?
a. two alleles code for blood types and four phenotypes are possible.
b. allele ia and ib are codominant, and allele i is recessive.
c. allele i is dominant over alleles ia and ib.
d. three alleles code for blood types and three phenotypes are possible.

In human blood types two alleles are inherited ,one from each parent.
If the allele is i it is a recessive trait.
Blood types possible: A, B, AB, O.

D. Is wrong because you don't inherit three alleles and there is more than just one outcome possible.
C. Is wrong because i is recessive and IA and IB are both dominate.
B. Is wrong because IA and IB are not codominant.

A. Is right because two alleles from parents. Alleles do code for blood types. and their are four phenotypes possible: A, B, AB, and O blood types.