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Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of fertilization through sexual reproduction until birth, hatching, or germination.
In humans, an embryo is generally considered to be between the first and the eighth week of development after fertilization〔(【引用サイトリンク】url=http://www.oxforddictionaries.com/definition/english/embryo )〕 and from then it is instead called a fetus. Some definitions consider embryological life to start at the third week of development to the eighth, when most organ systems are developing.
The development of the embryo is called embryogenesis. In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote, which possesses half the DNA of each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The result of this process is an embryo.
==Etymology==
First attested in English in the mid-14c., the word ''embryon'' derives from Medieval Latin ''embryo'', itself from Greek (''embruon''), lit. "young one",〔(ἔμβρυον ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕 which is the neuter of (''embruos''), lit. "growing in",〔(ἔμβρυος ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕 from ἐν (''en''), "in"〔(ἐν ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕 and βρύω (''bruō''), "swell, be full";〔(βρύω ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕 the proper Latinized form of the Greek term would be ''embryum''.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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