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.

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

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]

alternation of generations

A life cycle (e.g. mosses, ferns) in which a haploid generation alternates with a diploid generation.
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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
References in periodicals archive ?
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.
One question, left unanswered by Hofmeister, was how the alternation of generations of the 'higher cryptogams' or archegoniates related to the life histories of 'lower cryptogams' or thallophytes.
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?
Since, in evolution, the development of sex surely preceded alternation of generations, the gametophyte generation is considered, necessarily, to be older than the sporophyte generation (cf.
Brown (1935: 657-658) clearly believed, however, that "it is doubtful if any alternation of generations .

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