alternation of generations


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alternation of generations

n.
The regular alternation of forms or of mode of reproduction in the life cycle of an organism, such as the alternation between diploid and haploid phases, or between sexual and asexual reproductive cycles.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

alternation of generations

n
(Biology) the production within the life cycle of an organism of alternating asexual and sexual reproductive forms. It occurs in many plants and lower animals. Also called: metagenesis, heterogenesis, digenesis or xenogenesis
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

alterna′tion of genera′tions


n.
the alternation in an organism's life cycle of dissimilar reproductive forms, esp. the alternation of sexual with asexual generations.
[1855–60]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.

alternation of generations

A life cycle (e.g. mosses, ferns) in which a haploid generation alternates with a diploid generation.
Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.alternation of generations - the alternation of two or more different forms in the life cycle of a plant or animal
organic phenomenon - (biology) a natural phenomenon involving living plants and animals
digenesis, metagenesis - alternation of sexual and asexual generations
Based on WordNet 3.0, Farlex clipart collection. © 2003-2012 Princeton University, Farlex Inc.
References in periodicals archive ?
One very intriguing and significant historical discussion concerns the alternation of generations. For living things that display a remarkably distinct alternation of generations such as between haploid and diploid generations, to what extent are we dealing with distinct biological individualities?
This is called the alternation of generations in plants, as shown in Figure 12-3.
Microgametogenesis, which occurs inside the developed pollen grain, comprises the gametophyte stage, the gamete-producing organism in the alternation of generations. The haploid microspore nucleus divides mitotically to produce two haploid nuclei: the tube nucleus and the generative nucleus.
Steenstrup (1845) defined alternation of generations as "the remarkable, and till now inexplicable phenomenon of an animal producing an offspring, which at no times resembles its parent, but which, on the other hand, itself brings forth a progeny, which returns in its form and nature to the parent animal, so that the maternal animal does not meet with its own resemblance in its own brood, but in its descendants of the second, third, or fourth degree of generation" (p.
Although alternation of generations initially referred to the alternation of sexual and asexual forms in animals, the term is now almost exclusively associated with the life cycles of plants, specifically with the alternation of haploid gametophytes and diploid sporophytes.
In any event, in the context of an improved knowledge of putative land-plant ancestors, we may now appropriately ask again the question, which theory of alternation of generations (and sporophyte origin) in land plants is more plausible, the homologous theory or the antithetic theory?

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