Final answer:
The dihybrid cross that will produce a 1:1 phenotypic ratio is Aa Bb × aa bb. So, the correct answer is the third option.
Step-by-step explanation:
Among the dihybrid crosses listed, the one that will produce a 1:1 phenotypic ratio is Aa Bb × aa bb. This is because the combination of Aa Bb and aa bb genotypes will result in equal proportions of dominant and recessive phenotypes. For example, if you consider the traits of flower color (A/a) and seed shape (B/b), the resulting offspring from the Aa Bb × aa bb cross will have a 1:1 ratio of dominant (Aa Bb) to recessive (aa bb) phenotypes for both traits.
So, the correct answer is the third option.