Where does the embryo develop in a fertile egg?

The embryo develops in a fertile egg at the germinal disc, which is the specific area on the surface of the yolk where fertilization occurs. The germinal disc contains the blastodisc, which is critical for the development of the embryo. When the egg is fertilized, the sperm penetrates the germinal disc leading to the formation of the embryo.

Understanding the role of the germinal disc is essential for grasping the overall development process in avian biology. Other parts mentioned, such as the yolk sac, chalaza, and embryonic membrane, have different functions. The yolk sac provides nutrients to the developing embryo, the chalaza helps to anchor the yolk in place, and the embryonic membrane assists in protecting the embryo and facilitating gas exchange. However, the actual development of the embryo occurs at the germinal disc, making it the correct answer.