Final answer:
The appearance of a plant with the genotype PpTt would be purple flowers and tall. A Punnett square is used to predict the offspring genotypes and phenotypes of a cross between PpYY and ppYy pea plants, such as purple or white flowers with yellow peas.
Step-by-step explanation:
A plant with the genotype PpTt would have purple flowers and be tall. This is because the P allele for purple flowers is dominant over the p allele for white flowers, and the T allele for tall plants is dominant over the t allele for dwarf plants. As long as one dominant allele is present for each trait (P from the Pp genotype and T from the Tt genotype), the dominant phenotypes will be expressed.
Concerning the cross between PpYY and ppYy pea plants, the possible genotypes would be PpYY, PpYy, ppYY, and ppYy, as indicated by a 2x2 Punnett square. These would result in phenotypes of purple flowers with yellow peas and white flowers with yellow peas. A Punnett square analysis facilitates the understanding of inheritance patterns.