Work Step by Step
By the activation and inactivation of different sequences of the ABC genes, flowers can form. Expression of the A gene causes the formation of sepals only. Then, activation of both the A and B genes together form the petals. Switching off the A gene, keeping the B gene turned on, and then activating the C gene causes the stamens to form. Turning off the B gene and keeping the C gene activated causes the formation of the carpel.