into the male genitalia. Without the hormone, the cells would develop into the female genitalia despite the fact that the embryo's sex is male. In this way, the male sex hormone present in the mother acts as a permissive inducer.
While some inducers operate by activating a portion of the target cell's genes, others induce change by repressing a portion of the target cell's genes. Still other inducers have the characteristic of activating the genes in some cells while repressing the same genes in other cells. Through this system of activation and repression, inducers insure that only the appropriate number of cells are committed to each developing tissue or organ. During neurulation, for instance, induction insures that only the ectoderm of the neural tube has the capability of becoming nervous tissue and that only the ectoderm of the outer layer of the embryo will become the epidermis. Overall, the process of induction is a process of ongoing feedback. As one cell responds to inducers, it alters the environment of the cells within its proximity by releasing its own inducers. As a result, the environment of each cell constantly changes during the development of the embryo. Each change affects the activities of a cell's genes, channeling the cell toward the function it will play in the fully-developed organism.
