Embryonic Development in Animals & Humans
All animals, including humans, follow similar patterns of embryonic development after fertilization of the egg by sperm. Embryogenesis occurs from the first few rounds of cell division until the offspring is considered a fetus.
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Early Cell Division
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The earliest phase of embryonic development is when the fertilized egg undergoes rapid cell division, forming first a clump of cells and then a hollowed out ball called a blastula.
Layers
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After early cell division, the embryo separates into three layers, the ectoderm, mesoderm and endoderm, which will become all of the parts of the animal's body.
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Organ Formation
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After the layers have completely formed, the embryo starts developing organs. Often organs will grow and then disappear, such as the tail of a human embryo. Also, animals will differ in terms of what organs they will form because not all animals have the same structures. Some, for instance, will develop wings.
Location and Timing
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The beginnings of embryonic development may occur inside the mother's body or in eggs which she has laid outside her body to be fertilized, depending on the species. Embryonic development ends when the organism transforms into a fetus or larvae, after the basic organs are formed.
Genetics
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All embryonic development is controlled by genes inherited from the parents. Many genes are only active during embryonic development and are turned off permanently after this phase of life.
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References
Resources
- Photo Credit Image by Flickr.com, courtesy of lunar caustic
