A monohybrid cross yields a 3:1 phenotypic ratio in the F₂, if purple flower color is dominant and white is recessive.

The genotypic ratio is 1:2:1, since there are 2 types of purple-flowered plants: PP (homozygous) and Pp (heterozygous).

The true-breeding P generation must have identical alleles for that gene and are homozygous.

In the heterozygous F₁ and F₂ individuals, the dominant purple allele determines the phenotype.