 Their bodies are patterned by a system of switching which causes development of different features to begin earlier or later, to occur in this or that part of the embryo, and to continue for more or less time.The puzzle of how embryonic development was controlled began to be solved using the fruit fly "Drosophila melanogaster" as a model organism.The step-by-step control of its embryogenesis was visualized by attaching fluorescent dyes of different colours to specific types of protein made by genes expressed in the embryo.