A report on Alternation of generations

Diagram showing the alternation of generations between a diploid sporophyte (bottom) and a haploid gametophyte (top)
Gametophyte of the fern Onoclea sensibilis (the flat thallus at the bottom of the picture) with a descendant sporophyte beginning to grow from it (the small frond at the top of the picture).
Graphic referred in text.
Life cycle of Foraminifera showing alternation of generations.
Diagram of alternation of generations in liverworts.
Moss life cycle diagram
Hornwort life cycle diagram
<center>Diagram of alternation of generations in ferns.</center>
<center>A gametophyte (prothallus) of Dicksonia sp.</center>
<center>A sporophyte of Dicksonia antarctica.</center>
<center>The underside of a Dicksonia antarctica frond showing the sori, or spore-producing structures.</center>
Angiosperm life cycle
Tip of tulip stamen showing pollen (microgametophytes)
Plant ovules (megagametophytes): Gymnosperm ovule on left, angiosperm ovule (inside ovary) on right
Double fertilization

Predominant type of life cycle in plants and algae.

- Alternation of generations
Diagram showing the alternation of generations between a diploid sporophyte (bottom) and a haploid gametophyte (top)

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Several gametophytes growing in a terrarium.

Gametophyte

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Several gametophytes growing in a terrarium.
Pine gametophyte (outside) surrounding the embryo (inside)
Multiple examples of the variation of cell number in mature seed plant female gametophytes prior to fertilization. Each cell contains one nucleus unless depicted otherwise. A: Typical 7 celled, 8 nucleate angiosperm female gametophyte (ex. Tilia americana). B: Typical gymnosperm female gametophyte with many haploid somatic cells illustrated with a honeycomb grid and two haploid germ cells (ex. Ginkgo biloba). C: Abnormally large 10 celled, 16 nucleate angiosperm female gametophyte (ex. Peperomia dolabriformis). D: Abnormally small 4 celled, 4 nucleate angiosperm female gametophyte (ex. Amborella trichopoda). E: Unusual gymnosperm female gametophyte that is singled celled with many free nuclei surrounding a pictured central vacuole (ex. Gnetum gnemon). Blue: egg cell. Dark orange: synergid cell. Yellow: accessory cell. Green: antipodal cell. Peach: central cell. Purple: individual nuclei.

A gametophyte is one of the two alternating multicellular phases in the life cycles of plants and algae.

Plant

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Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae.

Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae.

Green algae from Ernst Haeckel's Kunstformen der Natur, 1904.
A variaty of fungi species
Dicksonia antarctica, a species of tree fern
A petrified log in Petrified Forest National Park, Arizona
Range of pangaea glossopteris.
The leaf is usually the primary site of photosynthesis in plants.
There is no photosynthesis in deciduous leaves in autumn.
Plant cell structure
The Venus flytrap, a species of carnivorous plant.
Mechanical harvest of oats.
Melocactus plants being used as medicine.
Timber in storage for later processing at a sawmill
A rose espalier at Niedernhall in Germany.
Capitals of ancient Egyptian columns decorated to resemble papyrus plants. (at Luxor, Egypt)
Barbara McClintock (1902–1992) was a pioneering cytogeneticist who used maize (corn) to study the mechanism of inheritance of traits.
Musk Thistle are invasive species in texas.

Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.

Spores produced in a sporic life cycle.

Spore

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Unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions.

Unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions.

Spores produced in a sporic life cycle.
Fresh snow partially covers rough-stalked feather-moss (Brachythecium rutabulum), growing on a thinned hybrid black poplar (Populus x canadensis). The last stage of the moss lifecycle is shown, where the sporophytes are visible before dispersion of their spores: the calyptra (1) is still attached to the capsule (3). The tops of the gametophytes (2) can be discerned as well. Inset shows the surrounding, black poplars growing on sandy loam on the bank of a kolk, with the detail area marked.
Asci of Morchella elata, containing ascospores
In plants, microspores, and in some cases megaspores, are formed from all four products of meiosis.
In contrast, in many seed plants and heterosporous ferns, only a single product of meiosis will become a megaspore (macrospore), with the rest degenerating.
Fossil plant spores (Scylaspora) from Silurian deposits of Sweden.
Tricolpate pollen of Ricinus
Spores of the moss Bartramia ithyphylla. (microscopic view, 400x)
Dehisced fern sporangia. (microscopic view, no spores are visible)
Spores and elaters from a horsetail. (Equisetum, microscopic view)
Fruit mold with spores and distinguishable cellular growth. (2000x)
Spore clusters, formed inside sporangia of the slime mold Reticularia olivacea, from pine forests of eastern Ukraine.
Internal surface of the peridium of the slime mold Tubifera dudkae with spores.

This cycle is known as alternation of generations.

Young sporophytes of the common moss Tortula muralis. In mosses, the gametophyte is the dominant generation, while the sporophytes consist of sporangium-bearing stalks growing from the tips of the gametophytes

Sporophyte

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Diploid multicellular stage in the life cycle of a plant or alga.

Diploid multicellular stage in the life cycle of a plant or alga.

Young sporophytes of the common moss Tortula muralis. In mosses, the gametophyte is the dominant generation, while the sporophytes consist of sporangium-bearing stalks growing from the tips of the gametophytes
Sporophytes of moss during spring
Diagram showing the alternation of generations between a diploid sporophyte (bottom) and a haploid gametophyte (top)
In flowering plants, the sporophyte comprises the whole multicellular body except the pollen and embryo sac
Cleistocarpous sporophyte of the moss Physcomitrella patens

This cycle is known as alternation of generations or alternation of phases.

Fern

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Member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers.

Member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers.

A fern unrolling a young frond
Ferns at the Royal Melbourne Botanical Gardens
Tree ferns, probably Dicksonia antarctica, growing in Nunniong, Australia
Tree ferns, Alsophila spinulosa,
Sporophylls of Acrostichum aureum
Ferns at Muir Woods, California
Close-up of a monarch fern sorus, showing its sporangium
Gametophyte (thalloid green mass) and sporophyte (ascendent frond) of Onoclea sensibilis
Blätter des Manns Walfarn. by Alois Auer, Vienna: Imperial Printing Office, 1853
Barnsley fern created using chaos game, through an Iterated function system (IFS).
Ferns in one of many natural Coast Redwood undergrowth settings Santa Cruz, CA
Fern bed under a forest canopy in woods near Franklin, Virginia
Fern growing on a wall
Silver fern or Alsophila dealbata, endemic to New Zealand
Adiantum philippense
{{Interlanguage link multi|Pyrrosia piloselloides|id|Pyrrosia piloselloides}}, dragon's scale, in Malaysia
Hymenophyllum nephrophyllum, the kidney fern
Tree fern, probably Dicksonia antarctica
Tree ferns, probably Dicksonia antarctica
"Filicinae" from Ernst Haeckel's Kunstformen der Natur, 1904
A young, newly formed fern frond
A tree fern unrolling a new frond
Fern leaf, probably Lomaria nuda
Leaf of fern
Nature prints in The Ferns of Great Britain and Ireland used fronds to produce the plates
Sporangia of Dryopteris filix-mas
Tree fern sporangia San Diego, CA
Sporangia on a leaflet
Epiphytic fern on the branch of Cephalotaxus wilsoniana

Like all land plants, they have a life cycle referred to as alternation of generations, characterized by alternating diploid sporophytic and haploid gametophytic phases.

In the first stage of sexual reproduction, "meiosis", the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During "fertilisation", haploid gametes come together to form a diploid zygote, and the original number of chromosomes is restored.

Sexual reproduction

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Type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes (haploid) combines with another to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid).

Type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes (haploid) combines with another to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid).

In the first stage of sexual reproduction, "meiosis", the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During "fertilisation", haploid gametes come together to form a diploid zygote, and the original number of chromosomes is restored.
An Australian emperor dragonfly laying eggs, guarded by a male
Flowers contain the sexual organs of flowering plants.
Puffballs emitting spores

This type of life cycle, involving alternation between two multicellular phases, the sexual haploid gametophyte and asexual diploid sporophyte, is known as alternation of generations.

A haploid set that consists of a single complete set of chromosomes (equal to the monoploid set), as shown in the picture above, must belong to a diploid species. If a haploid set consists of two sets, it must be of a tetraploid (four sets) species.

Ploidy

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Number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes.

Number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes.

A haploid set that consists of a single complete set of chromosomes (equal to the monoploid set), as shown in the picture above, must belong to a diploid species. If a haploid set consists of two sets, it must be of a tetraploid (four sets) species.

This is called alternation of generations.

Life cycle of a mosquito. An adult female mosquito lays eggs which develop through several stages to adulthood. Reproduction completes and perpetuates the cycle.

Biological life cycle

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Series of changes in form that an organism undergoes, returning to the starting state.

Series of changes in form that an organism undergoes, returning to the starting state.

Life cycle of a mosquito. An adult female mosquito lays eggs which develop through several stages to adulthood. Reproduction completes and perpetuates the cycle.
Zygotic meiosis
Gametic meiosis
Sporic meiosis
Life cycle of the apicomplexan, Babesia, Life cycle of the single-celled parasite Babesia, including the infection to humans

For plants and many algae, there are two multicellular stages, and the life cycle is referred to as alternation of generations.

In meiosis, the chromosome or chromosomes duplicate (during interphase) and homologous chromosomes exchange genetic information (chromosomal crossover) during the first division, called meiosis I. The daughter cells divide again in meiosis II, splitting up sister chromatids to form haploid gametes. Two gametes fuse during fertilization, forming a diploid cell with a complete set of paired chromosomes.

Meiosis

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Special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells.

Special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells.

In meiosis, the chromosome or chromosomes duplicate (during interphase) and homologous chromosomes exchange genetic information (chromosomal crossover) during the first division, called meiosis I. The daughter cells divide again in meiosis II, splitting up sister chromatids to form haploid gametes. Two gametes fuse during fertilization, forming a diploid cell with a complete set of paired chromosomes.
Meiosis Prophase I in mice. In Leptotene (L) the axial elements (stained by SYCP3) begin to form. In Zygotene (Z) the transverse elements (SYCP1) and central elements of the synaptonemal complex are partially installed (appearing as yellow as they overlap with SYCP3). In Pachytene (P) it's fully installed except on the sex chromosomes. In Diplotene (D) it disassembles revealing chiasmata. CREST marks the centromeres.
Schematic of the synaptonemal complex at different stages of prophase I and the chromosomes arranged as a linear array of loops.
Diplontic life cycle
Haplontic life cycle.
Overview of chromatides' and chromosomes' distribution within the mitotic and meiotic cycle of a male human cell

Consequently, this cycle is also known as the alternation of generations.

Algae

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Informal term for a large and diverse group of photosynthetic eukaryotic organisms.

Informal term for a large and diverse group of photosynthetic eukaryotic organisms.

False-color scanning electron micrograph of the unicellular coccolithophore Gephyrocapsa oceanica
title page of Gmelin's Historia Fucorum, dated 1768
The kelp forest exhibit at the Monterey Bay Aquarium: A three-dimensional, multicellular thallus
Rock lichens in Ireland
Floridian coral reef
Algae on coastal rocks at Shihtiping in Taiwan
Phytoplankton, Lake Chūzenji
Harvesting algae
Seaweed-fertilized gardens on Inisheer
Dulse, a type of edible seaweed
Algae bladder

These probably had an isomorphic alternation of generations and were probably filamentous.