Consider a gene with three alleles controlling coloration of a flowering plant. There are 3 possible phenotypes, corresponding to the following dominance hierarchy among the alleles: A1 is dominant to A2 and A3, and A2 is dominant to A3. Which of the following genotype pairs express the same phenotype?

A.
A2A2, A3A3

B.
A1A1, A3A3

C.
A1A2, A1A3

D.
A2A3, A1A3

This question depicts a gene coding for coloration in a flowering plant. The gene is controlled by multiple alleles, three specifically. The alleles are labelled A1, A2, and A3, with each coding for it's own respective trait.

According to the question, A1 is dominant over A2 and A3 i.e. A1 will always mask the phenotypic expression of A2 and A3 and express itself. Also, A2 is dominant over A3 i.e. A2 will always mask the phenotypic expression of A3. This overall means that the trait encoded by allele A3 will only be expressed when the same alleles are present.

To the question; since A1 is dominant over the other two alleles (A2 and A3), it will be phenotypically expressed ahead of them in a heterozygous state with both alleles. That is, A1A2 genotype will give rise to a phenotype encoded by A1. Also, A1A3 will produce a phenotype encoded by A1. Hence, genotypes A1A2 and A1A3 will express the same phenotypes.

A2A2 and A3A3 will express different phenotypes since they are both in a same alleles condition. Likewise for A1A1 and A3A3. A2A3 and A1A3 genotypes will express different phenotypes encoded by A2 and A1 respectively since they are both dominant over A3.