Skin tissue can become an amazing diversity of different organs, adapting to the biological needs of countless types of species. Simply by folding the tissue cells in different patterns—all controlled by a single master gene called EDA—a patch of skin can become a reptile's scale, a bird's feather, and even a mammal's mammary gland. This single gene controls the building blocks for some of the most important organs in the animal kingdom, all derived from the same type of cell.