How does incomplete dominance produce pink flowers in four-o’clock plants?

In four-o’clock plants (Mirabilis), pink flowers are produced through a phenomenon known as incomplete dominance. Unlike complete dominance, where one allele masks the expression of another, incomplete dominance occurs when the heterozygous offspring display a phenotype that is an intermediate blend of the two homozygous parents.12

When a homozygous red-flowered plant (RR) is crossed with a homozygous white-flowered plant (rr), the resulting F₁ generation is heterozygous (Rr). Because neither the red allele nor the white allele is fully dominant, the Rr genotype expresses itself as pink.12

This is not a permanent blending of genetic material, as evidenced by crossing these pink F₁ hybrids. Doing so yields an F₂ generation with a phenotypic ratio of 1 red (RR) : 2 pink (Rr) : 1 white (rr). This demonstrates that the original alleles remain discrete units of heredity that segregate during the formation of reproductive cells, confirming that the inheritance follows Mendelian mechanisms despite the intermediate appearance of the heterozygotes.12