Final answer:
The aspect of the phenotype of apetala2 agamous double mutants showing antagonistic interaction is the loss of floral organ identities, implying that each gene normally acts to suppress the function of the other. Epistasis is similarly demonstrated in mouse coat color where the gene for pigment production is epistatic to the agouti gene.
Step-by-step explanation:
The aspect of the phenotype of apetala2 agamous double mutants that indicates that these two genes act antagonistically is that in the presence of mutations in both the APETALA2 and AGAMOUS genes, the resulting phenotypes demonstrate a loss of organ identity in floral structures. This observation suggests that each gene usually acts to restrict or suppress the function of the other in the formation of flowers. In cases where one gene is meant to promote a certain floral organ identity and the other to inhibit it, the presence of mutations in both genes showcases a complete loss of these developmental instructions, resulting in flowers with unusual structures.
Epistasis can be seen with the example of coat color in mice. Normally, the agouti gene (A) and a separate gene for pigment production (C) work together to determine coat color. However, the recessive allele c is epistatic to the agouti gene, meaning that if a mouse has two copies of the c allele (cc), it will exhibit an albino phenotype, irrespective of the alleles present at the A locus.