Monohybrid Cross Problem Set

Problem 11: Codominant alleles: The human ABO markers

Human blood type is determined by codominant alleles. There are three different alleles, known as I^A, I^B, and i. The I^A and I^B alleles are codominant, and the i allele is recessive.

The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B individuals can be either homozygous (I^AI^A or I^BI^B, respectively), or heterozygous (I^Ai or I^Bi, respectively).

A woman with type A blood and a man with type B blood could potentially have offspring with which of the following blood types?

A. type A

B. type B

C. type AB

D. type O

E. all of the above

But if the man was type O rather than type B, offspring of type B and type AB would not be possible.