Final answer:
Plants with the ccPp genotype have white petals due to the recessive nature of the 'c' allele, which does not produce purple pigmentation, while CcPp plants have at least one dominant 'C' allele for purple petals. The genotypes and phenotypes for a cross between PpYY and ppYy or PpYY and ppyy plants can be determined using a 2x2 Punnett square.
Step-by-step explanation:
An explanation for why plants with the ccPp genotype have white petals while plants with the CcPp genotype have purple petals is due to the fact that the presence of the 'C' allele is necessary for purple pigmentation. The 'c' allele is recessive and when in a homozygous state (cc), it is unable to produce the pigmentation needed for purple flowers, resulting in white petals. In contrast, the CcPp genotype has at least one dominant 'C' allele, leading to the expression of purple petals. The P gene is not relevant to the petal color in this example, as it represents a different trait (pea color).
The possible genotypes for a cross between PpYY and ppYy plants are: PpYY, PpYy, ppYY, and ppYy. Phenotypically, this would yield plants with purple flowers and yellow peas, as well as those with white flowers and yellow peas. This can be analyzed using a 2x2 Punnett square.
When considering a different cross, between PpYY and ppyy plants, the possible genotypes include: PPYY, PpYy, ppYY, and ppyy, with associated phenotypes being purple flowers with yellow peas, white flowers with yellow peas, and white flowers with green peas. The analysis of this cross also requires a 2x2 Punnett square.