alternation of generations

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

(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

the alternation in an organism's life cycle of dissimilar reproductive forms, esp. the alternation of sexual with asexual generations.

[1855–60]

alternation of generations

A life cycle (e.g. mosses, ferns) in which a haploid generation alternates with a diploid generation.

ThesaurusAntonymsRelated WordsSynonymsLegend:

Noun

alternation of generations - the alternation of two or more different forms in the life cycle of a plant or animal

heterogenesis, xenogenesis

organic phenomenon - (biology) a natural phenomenon involving living plants and animals

digenesis, metagenesis - alternation of sexual and asexual generations

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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?

BIOLOGICAL INDIVIDUALITY: Integrating Scientific, Philosophical, and Historical Perspectives

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.

Chapter 12: Sexual reproduction and inheritance

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.

Homologous versus antithetic alternation of generations and the origin of 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?

Two theories of origin of the land-plant sporophyte: which is left standing?