Alternation of generations

alternation of generationalternatingdiplohaplonticlife cyclesporophyte generationalteration of generationsalternates generationsalternating generationsalternating multicellular generationsalternating phases
This article describes alternation of generations in plants; for a similar phenomenon in animals see Heterogamy Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages.wikipedia
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Biological life cycle

life cyclelifecyclelife history
Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages.
For plants and many algae, there are two multicellular stages, and the life cycle is referred to as alternation of generations.

Plant

Plantaeplantsflora
Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages.
Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.

Gametophyte

gametophytesgametophyticmegagametophyte
In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs.
A gametophyte is one of the two alternating phases in the life cycle of plants and algae.

Spore

sporessporulationsporulate
A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.
This cycle is known as alternation of generations.

Sporophyte

sporophyticsporophytessporphytic
In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs.
This cycle is known as alternation of generations or alternation of phases.

Vascular plant

vascular plantshigher plantsvascular
By contrast, in all modern vascular plants the gametophyte is less well developed than the sporophyte, although their Devonian ancestors had gametophytes and sporophytes of approximately equivalent complexity.

Algae

algaalgalfilamentous algae
Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages. This cycle, from gametophyte to gametophyte (or equally from sporophyte to sporophyte), is the way in which all land plants and many algae undergo sexual reproduction.
These probably had an isomorphic alternation of generations and were probably filamentous.

Red algae

Rhodophytared algared
Although most often coinciding, morphological alternation and nuclear phases alternation are sometimes independent of one another, e.g., in many red algae, the same nuclear phase may correspond to two diverse morphological generations. The term "plants" is taken here to mean the Archaeplastida, i.e. the glaucophytes, red and green algae and land plants.
The red algal life history is typically an alternation of generations that may have three generations rather than two.

Sexual reproduction

sexuallysexualreproduce sexually
This cycle, from gametophyte to gametophyte (or equally from sporophyte to sporophyte), is the way in which all land plants and many algae undergo sexual reproduction.
Plants have an alternation of generations where the sporophyte phase is succeeded by the gametophyte phase.

Meiosis

meioticsyzygymeiosis I
A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.
Consequently, this cycle is also known as the alternation of generations.

Fern

PolypodiopsidafernsPolypodiophyta
In ferns the gametophyte is a small flattened autotrophic prothallus on which the young sporophyte is briefly dependent for its nutrition.
Like all land plants, they have a life cycle referred to as alternation of generations, characterized by alternating diploid sporophytic and haploid gametophytic phases.

Japetus Steenstrup

SteenstrupJohannes SteenstrupJohannes Japetus Smith Steenstrup
Initially, Chamisso and Steenstrup described the succession of differently organized generations (sexual and asexual) in animals as "alternation of generations", while studying the development of tunicates, cnidarians and trematode animals.
He worked on a great many subjects, including cephalopods, and also in genetics, where he discovered the principle of the alternation of generations in some parasitic worms in 1842.

Wilhelm Hofmeister

HofmeisterHofmeister, Wilhelm FriedrichbenediktWilhelm Friedrich Benedikt Hofmeister
Wilhelm Hofmeister demonstrated the morphological alternation of generations in plants, between a spore-bearing generation (sporophyte) and a gamete-bearing generation (gametophyte).
Nevertheless, he was only 27 when he published his ground-breaking monograph on the alternation of generations in plants.

Gamete

gametesgameticreproductive cells
At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes.
However, since plants have an alternation of diploid and haploid generations some differences exist.

Cnidaria

cnidariancnidarianscnidarian venoms
Initially, Chamisso and Steenstrup described the succession of differently organized generations (sexual and asexual) in animals as "alternation of generations", while studying the development of tunicates, cnidarians and trematode animals.
This phenomenon of succession of differently organized generations (one asexually reproducing, sessile polyp, followed by a free-swimming medusa or a sessile polyp that reproduces sexually) is sometimes called "alternation of asexual and sexual phases" or "metagenesis", but should not be confused with the alternation of generations as found in plants.

Bryophyte

bryophytesBryophytamosses
For example, in all bryophytes the gametophyte generation is dominant and the sporophyte is dependent on it.
Like all land plants (embryophytes), bryophytes have life cycles with alternation of generations.

Embryophyte

land plantsland plantEmbryophyta
The term "plants" is taken here to mean the Archaeplastida, i.e. the glaucophytes, red and green algae and land plants.
In common with all groups of multicellular algae they have a life cycle which involves 'alternation of generations'.

Tunicate

TunicatatunicatesUrochordata
Initially, Chamisso and Steenstrup described the succession of differently organized generations (sexual and asexual) in animals as "alternation of generations", while studying the development of tunicates, cnidarians and trematode animals.
Salps also have a complex lifecycle with an alternation of generations.

Prothallium

prothallusprothalliprothallia
In ferns the gametophyte is a small flattened autotrophic prothallus on which the young sporophyte is briefly dependent for its nutrition.
Spore-bearing plants, like all plants, go through a life-cycle of alternation of generations.

Green algae

green algagreengreen algal
The term "plants" is taken here to mean the Archaeplastida, i.e. the glaucophytes, red and green algae and land plants.
The diplobiontic species, such as Ulva, follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic (having the same morphology).

Ploidy

diploidhaploid2n
In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs.
This is called alternation of generations.

Archaeplastida

archaeplastidangreen and red algaePrimoplantae
Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages. The term "plants" is taken here to mean the Archaeplastida, i.e. the glaucophytes, red and green algae and land plants.

Heterokont

HeterokontaStramenopilesstramenopile
Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages.

Chromosome

chromosomeschromosomalChromosomal number
In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs.

Mitosis

mitoticmitosesmitotic division
At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes.