The frequency of genotypes and phenotypes in the offspring is based on probability.
All the F₁ offspring of a monohybrid cross between true-breeding white (homozygous recessive, pp) and purple (homozygous dominant, PP) parents are purple heterozygotes (Pp).
The F₂ individuals exhibit a dominant : recessive phenotype ratio of 3 : 1.
The genotype ratio is 1 PP : 2 Pp : 1 pp.   Exercise: