Figure 14.12: ABC Model for Gene Expression and Morphogenesis in Arabidopsis thaliana Flowers (A) The four organs of a flower—sepals (pink), petals (purple), stamens (green), and carpels (yellow)—grow in whorls that develop from the floral meristem. (B) Floral organs are determined by three classes of genes whose polypeptide products combine in pairs to form transcription factors. (C) Combinations of polypeptide subunits in transcription factors activate gene expression for specific organs.