16. A young woman has a question about ABO blood types. She knows that she is type O but also knows that one of
her parents is type AB and the other is type B. Adultery or adoption are not possible, so the woman wonders how her blood type could have arisen. From the knowledge you’ve gained in genetics class, which of the following is a valid way to explain genetically how she received this seemingly impossible blood phenotype.
a. This is due to codominance, where the alleles for blood type are both expressed in the phenotype.
b. This is due to phenocopy, where the blood antigen genes mimic each other in the phenotype.
c. This is due to epistasis, where expression of an independent gene has an effect on the expression of blood type antigens and the resulting blood phenotype.
d. This is genetically impossible to happen as there is no situation where these alleles can make an O blood phenotype.