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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.〔Barnes, Richard Stephen Kent (2001). ''(The Invertebrates: A Synthesis )''. Wiley-Blackwell, p. 347. ISBN 978-0-632-04761-1.〕 The amount of yolk in an egg cell affects the developmental processes that follow fertilization. Apart from animals, other organisms, like algae, specially in the oogamous, can also accumulate resources in their female gametes. In gymnosperms, the remains of the female gametophyte serve also as food supply, and in flowering plants, the endosperm. == Chicken egg yolk == In the avian egg, the yolk usually is some shade of yellow in colour. It is spherical and is suspended in the egg white (known alternatively as ''albumen'' or ''glair''/''glaire'') by one or two spiral bands of tissue called the chalazae. Prior to fertilization, the yolk is a single cell, the ovum or egg cell, one of the few single cells that can be seen by the naked eye.〔Patten, B. M. (1951). ''(Early Embryology of the Chick )'', 4th edition. McGraw-Hill, New York, p. 17.〕 This fact was discovered by Hoyer in 1858.〔Callebaut, M. ''(Historical evolution of preformistic versus neoformistic (epigenetic) thinking in embryology )''.〕 After the fertilization, the cleavage leads to the formation of the germinal disc. As a food, chicken egg yolks are a major source of vitamins and minerals. They contain all of the egg's fat and cholesterol, and about one-half of the protein. If left intact while cooking fried eggs, the yellow yolk surrounded by a flat blob of whites creates a distinctive sunny-side up form. Mixing the two components together before frying results in a pale yellow mass, as in omelettes and scrambled eggs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yolk」の詳細全文を読む スポンサード リンク
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