Final answer:
When crossing two iris plants with medium-size leaves and pink flowers, a Punnett square can predict four distinct phenotypes in the offspring: large leaves with red flowers, medium leaves with pink flowers, small leaves with white flowers, and combinations in between. For a cross of PpYY and ppYy in pea plants, a 2x2 Punnett square is used, yielding phenotypes of purple flowers with yellow peas and white flowers with yellow peas.
Step-by-step explanation:
Genetics and Punnett Square Analysis
When crossing two plants with medium-sized leaves (P') and pink flowers (RR'), we can predict the expected phenotypes using a Punnett square for each trait. For the leaf size, represented by PP (large leaves), P'P' (small leaves), and PP' (medium leaves), a Punnett square between two PP' plants would result in three genotypes: 1 PP (1/4 of the offspring), 2 PP' (1/2), and 1 P'P' (1/4). For flower color, with the genotypes RR (red), R'R' (white), and RR' (pink), another Punnett square for two RR' plants would give similar results: 1 RR (1/4 of the offspring), 2 RR' (1/2), and 1 R'R' (1/4).
Combining the calculations for both traits, there would be a total of nine different genotypic combinations resulting in four distinct phenotypes: large leaves with red flowers, medium leaves with pink flowers, small leaves with white flowers, and the combinations in between. If there are 640 seedlings, expected numbers for each phenotype can be obtained by multiplying the total number by the probability of each phenotype.
To predict the phenotype and genotype of the offspring from a cross between PpYY and ppYy plants, we would need a Punnett square with 4 squares, which is a simple 2x2 grid. The possible genotypes would be PpYY, PpYy, ppYY, ppYy, and the phenotypes would be purple flowers with yellow peas, and white flowers with yellow peas. This example illustrates the inheritance of two independently assorted traits in a dihybrid cross.