How the developmental process of an animal embryo is controlled is one of the major unsolved problems in biology. Although how the embryo develops has been genetically determined, the genes themselves cannot directly explain the generation of differences in different parts of an organism. This is because the genetic material in most cells of an organism can be assumed to be the same. In other words, the genes only provide a blueprint for the final product. From the fertilization of the egg to birth, there must be a mechanism which physically translates the genetic information and governs the developmental process. But, what is that mechanism?