Phenotype and genotype.
<P>
   A  monohybrid  cross  yields  a  3:1  phenotypic ratio in the F[2], if
   purple flower color is dominant and white is recessive.
<P>
   The   genotypic   ratio   is   1:2:1,  since  there  are  2  types  of
   purple-flowered plants: PP (homozygous) and Pp (heterozygous).
<P>
   The  true-breeding  P  generation must have identical alleles for that
   gene and are homozygous.
<P>
   In  the  heterozygous  F[1]  and F[2] individuals, the dominant purple
   allele determines the phenotype.