The yolk is a part of an egg (or just of the egg cell in non-egg-laying animals) that feeds the developing embryo in animals. In whole eggs, 43% of the protein comes from the yolk.Also known as deutoplasm, this food material is accumulated during oogenesis, together with RNA molecules and other substances. These may be synthesized by the oocyte itself or by the cytoplasm of other non-germ cells.