Final answer:
The phenotypic ratio resulting from an Aa × Aa cross assuming complete dominance is 3:1, with three-quarters expressing the dominant phenotype and one-quarter expressing the recessive phenotype.
Step-by-step explanation:
When you cross two heterozygous individuals with the genotype Aa, and assuming complete dominance for the trait, the phenotypic ratio of the offspring will be 3:1. This means that three-quarters of the offspring are expected to display the dominant phenotype and one-quarter will display the recessive phenotype. This is derived from the Mendelian inheritance principles.
The genotypic ratio from the same Aa × Aa cross, as described by Mendel's laws, will be 1:2:1. This translates to one AA, two Aa (including aA which is the same as Aa), and one aa. Combining AA and Aa which express the dominant trait, we arrive at a 3:1 phenotypic ratio, which means, in a group of four offspring, approximately three will show the dominant trait and one will show the recessive trait.