Final answer:
The phenotypic ratio for the offspring of a cross between a tall purple pea plant and a dwarf pea plant heterozygous for purple color can be determined using a Punnett Square.
Step-by-step explanation:
When a tall purple pea plant dihybrid for height and color is crossed with a dwarf pea plant heterozygous for purple color, the Punnett Square can be used to determine the phenotypic and genotypic ratios for the offspring.
The genotype of the tall purple pea plant is TtPp and the genotype of the dwarf pea plant is ttpp.
The Punnett Square for this cross would look like this:
TtPpTtppttppTtPpttppTtppTtpp
The phenotypic ratio is 1:1 for tall purple plants to tall plants with white flowers.