In 4 ‘o’clock plants, the crossing of pure-bred red and white flowered parental stocks produced pink flowered plants. This type of genotypic expression is called
Incomplete dominance
Incomplete dominance was first observed in 4 ‘o’ clock plant. The allele responsible for red colour does not completely dominate the allele for white. The new phenotype pink arises by a “blend” of the dominant and recessive phenotypes.