 The giraffe does not have a gene for a long neck, any more than the elephant has a gene for a big body.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.