Embryo

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Definition

Noun

  • 1. The offspring of an animal before its birth (or its emergence from the egg): a. of man. In mod. technical language restricted to ‘the ftus in utero before the fourth month of pregnancy’ (Syd. Soc. Lex.) (now, before the third month).
b. of animals.
  • 2. Bot. ‘The rudimentary plant contained in the seed’ (Syd. Soc. Lex.).
  • 3. Chem. A metal or other chemical substance not disengaged from its native state of combination. Also attrib. Obs.
  • 4. fig. A thing in its rudimentary stage or first beginning; a germ; that which is still in idea as opposed to what has become actual in fact.
b. in embryo: in an undeveloped stage; ‘that is to be’. [? orig. Lat., from EMBRYON.]
  • 5. attrib. and Comb., as embryo-chick, -child, -germ, -life, -plant, -stage, -state; also embryo-bud, ‘an adventitious bud, when enclosed in the bark, as in the cedar of Lebanon’ (Syd. Soc. Lex.); embryo-cell, the first cell of the fecundated animal ovum; also in Bot. the germ in the embryo-sac of ferns, mosses, etc.; embryo-sac, Bot., a cavity in the ovule or the archegonium of a plant, within which the embryo is produced.

Adjective

[From the attrib. use of the n.] That is still in germ; immature, unformed, undeveloped.

Description

An embryo (irregularly from Greek: ἔμβρυον, plural ἔμβρυα, lit. "that which grows," from en- "in" + bryein "to swell, be full"; the proper Latinate form would be embryum) is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. In humans, it is called an embryo until about eight weeks after fertilization (i.e. ten weeks LMP), and from then it is instead called a fetus.

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 that has half of the DNA of each of two parents. The resulting embryo derives 50 percent of its genetic makeup from each parent. 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.

See also