Final answer:
Using a 4x4 Punnett square for the dihybrid cross TtYy x TtYy, we predict a phenotypic ratio of 9 tall yellow:3 tall green:3 dwarf yellow:1 dwarf green offspring, following Mendelian principles.
Step-by-step explanation:
In the cross TtYy x TtYy, we are looking at a dihybrid cross where each parent has two traits with two alleles. For such a cross, a larger Punnett square is needed that combines the possibilities for both traits. To determine the phenotypic ratio of the offspring, we look at the dominant and recessive combinations of each trait. Tall (T) is dominant over dwarf (t), and yellow (Y) is dominant over green (y). Using a 4x4 Punnett square to represent the combinations, we can predict the offspring's phenotypes. We would find the following phenotypic ratio: 9 tall yellow, 3 tall green, 3 dwarf yellow, and 1 dwarf green. This is because the tall or yellow traits will be expressed whenever their dominant allele is present.
Through Mendelian genetics, we understand that a dihybrid cross between heterozygous individuals with two traits yields a phenotypic ratio of 9:3:3:1. Since T and Y are dominant traits, the offspring will show tall or yellow phenotypes whenever these alleles are present. This leads to the expected phenotypic outcomes, where the majority of offspring are tall with yellow seeds, some are tall with green seeds, some are dwarf with yellow seeds, and a minority are dwarf with green seeds.