ABC model of flower development

Scientists have found through knocking out certain genes what genes code for the expression of given flower parts. While one gene codes for sepals, multiple genes code for the expression of other flower parts. By knocking out one of the genes in mutants, scientists discovered which coded for what. For example, when they removed the C class of genes from a mutant, it exhibited an extra set of sepals where it should have had petals, and an extra set of carpals where it should have had stamens.

A expressed alone results in sepals. A and B together express themselves just inside the sepals to create petals- if the B gene is knocked out, the plant will create sepals. B and C together express as stamens, without B, C will revert to expressing carpals. If the B gene is knocked out, the plant will exhibit mutant extra carpals in place of stamens. C by itself will express a carpal in the center of the flower as it is in unaltered wildtype plants.