EOC Biology STAAR Test Prep
In humans blood type is determined by the A, B, and O alleles. The A and B alleles are codiminant to each other and dominant over the O allele. An individual with the AO genotype and an individual with the BO genotype can produce offspring with which of the following phenotypes.
O only
A or B only
A, B or O only
A, B, AB, or O
Please explain, also this is not a test its a test PREP

We can start by visualizing all the possible genotypes of the offspring by drawing a Punnett square, which is a visual representation of the different possible combinations of alleles:

Individual 1 = AO, Individual 2 = BO

A O

B AB BO

O AO OO

Here we can see that there are 4 possible genotypes: AB, BO, AO and OO based on the alleles of the parents. Now we can match the genotypes to phenotypes to answer the question:

A and B are codominant, meaning that both will be expressed equally if both are present. Therefore the genotype AB will result in an AB phenotype.

Next, since A and B are both dominant over O, they are the alleles that will be expressed in the phenotype if paired with an O. This means that the genotype AO will result in an A phenotype, and likewise, genotype BO will result in phenotype B.

Finally in the genotype OO, although O is a recessive allele, there are no dominant alleles here to mask them, therefore O is expressed in the phenotype.

Hence, from the genotypes AO and BO, the possible offspring genotypes are AB, BO, AO and OO, translating to the possible phenotypes: A, B, AB or O.

Hope this helped!