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 IA, IB, and i. The IA and IB 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 (IAIA or IBIB, respectively), or heterozygous (IAi or IBi, 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?


Blood type and genotype
The relationship between blood type (phenotype) and genotype is shown in the table to the left. The mother (blood type A) and father (blood type B) could be either homozygous or heterozygous .

Type A and type B cross
Four different genetic crosses are possible. All four crosses must be considered to determine all potential offspring. However, one cross (IAi mother x IBi father) is most informative.

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Thursday, October 1, 1998
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