What does alternation of generations in plants refer to

Reproductive cycle of plants and algae

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

Alternation of generations (also known equally metagenesis or heterogenesis)^[one] is the predominant type of life cycle in plants and algae. It consists of a multicellular haploid sexual stage, the gametophyte, which has a unmarried fix of chromosomes alternate with a multicellular diploid asexual phase, the sporophyte which has two sets of chromosomes.

A mature sporophyte produces haploid spores by meiosis, a procedure which reduces the number of chromosomes to half, from two sets to one. The resulting haploid spores germinate and abound into multicellular haploid gametophytes. At maturity, a gametophyte produces gametes by mitosis, the normal process of jail cell division in eukaryotes, which maintains the original number of chromosomes. Ii haploid gametes (originating from different organisms of the same species or from the aforementioned organism) fuse to produce a diploid zygote, which divides repeatedly by mitosis, developing into a multicellular diploid sporophyte. This cycle, from gametophyte to sporophyte (or equally from sporophyte to gametophyte), is the fashion in which all state plants and most algae undergo sexual reproduction.

The relationship between the sporophyte and gametophyte phases varies amidst different groups of plants. In the majority of algae, the sporophyte and gametophyte are split up contained organisms, which may or may not have a similar advent. In liverworts, mosses and hornworts, the sporophyte is less well developed than the gametophyte and is largely dependent on information technology. Although moss and hornwort sporophytes can photosynthesise, they require additional photosynthate from the gametophyte to sustain growth and spore development and depend on it for supply of water, mineral nutrients and nitrogen.^{[2] [3]} Past 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.^[4] In ferns the gametophyte is a small flattened autotrophic prothallus on which the immature sporophyte is briefly dependent for its diet. In flowering plants, the reduction of the gametophyte is much more extreme; it consists of simply a few cells which grow entirely inside the sporophyte.

Animals develop differently. They directly produce haploid gametes. No haploid spores capable of dividing are produced, so by and large there is no multicellular haploid phase. (Some insects have a sex-determining system whereby haploid males are produced from unfertilized eggs; nevertheless females produced from fertilized eggs are diploid.)

Life cycles of plants and algae with alternating haploid and diploid multicellular stages are referred to as diplohaplontic (the equivalent terms haplodiplontic, diplobiontic and dibiontic are likewise in employ, as is describing such an organism as having a diphasic ontogenesis^[5]). Life cycles, such as those of animals, in which in that location is merely a diploid multicellular stage are referred to every bit diplontic. Life cycles in which there is only a haploid multicellular phase are referred to as haplontic.

Definition [edit]

Alternation of generations is defined as the alternation of multicellular diploid and haploid forms in the organism's life wheel, regardless of whether these forms are free-living.^[6] In some species, such equally the alga Ulva lactuca, the diploid and haploid forms are indeed both free-living independent organisms, essentially identical in appearance and therefore said to be isomorphic. The costless-pond, haploid gametes class a diploid zygote which germinates into a multicellular diploid sporophyte. The sporophyte produces costless-pond haploid spores by meiosis that germinate into haploid gametophytes.^[7]

However, in another groups, either the sporophyte or the gametophyte is very much reduced and is incapable of free living. For instance, in all bryophytes the gametophyte generation is dominant and the sporophyte is dependent on information technology. By dissimilarity, in all modernistic vascular state plants the gametophytes are strongly reduced, although the fossil show indicates that they were derived from isomorphic ancestors.^[4] In seed plants, the female gametophyte develops totally inside the sporophyte, which protects and nurtures it and the embryonic sporophyte that it produces. The pollen grains, which are the male gametophytes, are reduced to only a few cells (merely three cells in many cases). Here the notion of two generations is less obvious; as Bateman & Dimichele say "[s]porophyte and gametophyte effectively office as a unmarried organism".^[8] The alternative term 'alternation of phases' may then be more appropriate.^[ix]

History [edit]

Debates most alternation of generations in the early twentieth century can be confusing because various ways of classifying "generations" co-exist (sexual vs. asexual, gametophyte vs. sporophyte, haploid vs. diploid, etc.).^[ten]

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.^[10] This miracle is also known as heterogamy. Before long, the term "alternation of generations" is virtually exclusively associated with the life cycles of plants, specifically with the alternation of haploid gametophytes and diploid sporophytes.^[10]

Wilhelm Hofmeister demonstrated the morphological alternation of generations in plants,^[11] between a spore-bearing generation (sporophyte) and a gamete-bearing generation (gametophyte).^{[12] [xiii]} By that time, a debate emerged focusing on the origin of the asexual generation of land plants (i.east., the sporophyte) and is conventionally characterized as a conflict between theories of antithetic (Čelakovský, 1874) and homologous (Pringsheim, 1876) alternation of generations.^[10] Čelakovský coined the words sporophyte and gametophyte.^{[ commendation needed ]}

Eduard Strasburger (1874) discovered the alternation betwixt diploid and haploid nuclear phases,^[10] as well chosen cytological alternation of nuclear phases.^[14] Although most oft coinciding, morphological alternation and nuclear phases alternation are sometimes independent of i another, eastward.g., in many red algae, the aforementioned nuclear phase may correspond to two diverse morphological generations.^[14] In some ferns which lost sexual reproduction, there is no change in nuclear phase, but the alternation of generations is maintained.^[fifteen]

Alternation of generations in plants [edit]

Key elements [edit]

The diagram above shows the primal elements of the alternation of generations in plants. The many variations found in different groups of plants are described by use of these concepts afterwards in the article. Starting from the right of the diagram, the processes involved are as follows:^[16]

• Two single-celled haploid gametes, each containing north unpaired chromosomes, fuse to form a single-celled diploid zygote, which now contains n pairs of chromosomes, i.east. 2n chromosomes in total.
• The single-celled diploid zygote germinates, dividing by the normal process (mitosis), which maintains the number of chromosomes at 2n. The result is a multi-cellular diploid organism, called the sporophyte (because at maturity information technology produces spores).
• When it reaches maturity, the sporophyte produces i or more sporangia (atypical: sporangium) which are the organs that produce diploid spore mother cells (sporocytes). These divide past a special process (meiosis) that reduces the number of chromosomes by a half. This initially results in four single-celled haploid spores, each containing n unpaired chromosomes.
• The single-celled haploid spore germinates, dividing by the normal process (mitosis), which maintains the number of chromosomes at n. The result is a multi-cellular haploid organism, called the gametophyte (because it produces gametes at maturity).
• When it reaches maturity, the gametophyte produces 1 or more gametangia (singular: gametangium) which are the organs that produce haploid gametes. At least 1 kind of gamete possesses some mechanism for reaching another gamete in society to fuse with it.

The 'alternation of generations' in the life cycle is thus between a diploid (2n) generation of sporophytes and a haploid (n) generation of gametophytes.

Gametophyte of the fern Onoclea sensibilis (the flat thallus at the lesser of the pic) with a descendant sporophyte beginning to abound from it (the small frond at the top of the picture).

The situation is quite unlike from that in animals, where the cardinal process is that a diploid (iin) individual direct produces haploid (n) gametes by meiosis. In animals, spores (i.eastward. haploid cells which are able to undergo mitosis) are not produced, so there is no asexual multi-cellular generation. Some insects have haploid males that develop from unfertilized eggs, but the females are all diploid.

Variations [edit]

The diagram shown higher up is a proficient representation of the life cycle of some multi-cellular algae (due east.thousand. the genus Cladophora) which take sporophytes and gametophytes of nigh identical appearance and which do non accept different kinds of spores or gametes.^[17]

However, in that location are many possible variations on the fundamental elements of a life cycle which has alternation of generations. Each variation may occur separately or in combination, resulting in a bewildering variety of life cycles. The terms used by botanists in describing these life cycles can be as bewildering. As Bateman and Dimichele say "[...] the alternation of generations has get a terminological morass; ofttimes, one term represents several concepts or one concept is represented by several terms."^[xviii]

Possible variations are:

• Relative importance of the sporophyte and the gametophyte.
  • Equal (homomorphy or isomorphy).
    Filamentous algae of the genus Cladophora, which are predominantly constitute in fresh water, accept diploid sporophytes and haploid gametophytes which are externally duplicate.^[xix] No living country establish has equally dominant sporophytes and gametophytes, although some theories of the development of alternation of generations suggest that bequeathed land plants did.
  • Unequal (heteromorphy or anisomorphy).

    

    • Dominant gametophyte (gametophytic).
      In liverworts, mosses and hornworts, the dominant course is the haploid gametophyte. The diploid sporophyte is not capable of an contained existence, gaining most of its diet from the parent gametophyte, and having no chlorophyll when mature.^[20]

      

    • Ascendant sporophyte (sporophytic).
      In ferns, both the sporophyte and the gametophyte are capable of living independently, only the dominant form is the diploid sporophyte. The haploid gametophyte is much smaller and simpler in structure. In seed plants, the gametophyte is even more reduced (at the minimum to only three cells), gaining all its diet from the sporophyte. The farthermost reduction in the size of the gametophyte and its retention within the sporophyte means that when applied to seed plants the term 'alternation of generations' is somewhat misleading: "[s]porophyte and gametophyte effectively function as a single organism".^[8] Some authors accept preferred the term 'alternation of phases'.^[nine]
• Differentiation of the gametes.
  • Both gametes the same (isogamy).
    Like other species of Cladophora, C. callicoma has flagellated gametes which are identical in appearance and ability to move.^[xix]
  • Gametes of two distinct sizes (anisogamy).
    • Both of similar motion.
      Species of Ulva, the bounding main lettuce, have gametes which all have ii flagella and so are motile. However they are of 2 sizes: larger 'female' gametes and smaller 'male' gametes.^[21]
    • 1 large and sessile, one small and motile (oogamy). The larger sessile megagametes are eggs (ova), and smaller motile microgametes are sperm (spermatozoa, spermatozoids). The degree of motility of the sperm may be very limited (every bit in the example of flowering plants) just all are able to move towards the sessile eggs. When (as is near always the case) the sperm and eggs are produced in different kinds of gametangia, the sperm-producing ones are called antheridia (atypical antheridium) and the egg-producing ones archegonia (singular archegonium).

      

      Gametophyte of Pellia epiphylla with sporophytes growing from the remains of archegonia.

      • Antheridia and archegonia occur on the same gametophyte, which is then called monoicous. (Many sources, including those concerned with bryophytes, apply the term 'monoecious' for this situation and 'dioecious' for the opposite.^{[22] [23]} Here 'monoecious' and 'dioecious' are used but for sporophytes.)
        The liverwort Pellia epiphylla has the gametophyte as the dominant generation. It is monoicous: the small ruby sperm-producing antheridia are scattered along the midrib while the egg-producing archegonia grow nearer the tips of divisions of the plant.^[24]
      • Antheridia and archegonia occur on dissimilar gametophytes, which are then chosen dioicous.
        The moss Mnium hornum has the gametophyte as the dominant generation. Information technology is dioicous: male plants produce simply antheridia in terminal rosettes, female person plants produce only archegonia in the class of stalked capsules.^[25] Seed plant gametophytes are also dioicous. Still, the parent sporophyte may be monoecious, producing both male person and female gametophytes or dioecious, producing gametophytes of one gender but. Seed plant gametophytes are extremely reduced in size; the archegonium consists just of a small number of cells, and the entire male gametophyte may be represented by only ii cells.^[26]
• Differentiation of the spores.
  • All spores the aforementioned size (homospory or isospory).
    Horsetails (species of Equisetum) have spores which are all of the same size.^[27]
  • Spores of two distinct sizes (heterospory or anisospory): larger megaspores and smaller microspores. When the 2 kinds of spore are produced in different kinds of sporangia, these are called megasporangia and microsporangia. A megaspore frequently (but not ever) develops at the expense of the other 3 cells resulting from meiosis, which abort.
    • Megasporangia and microsporangia occur on the aforementioned sporophyte, which is then called monoecious.
      Nearly flowering plants autumn into this category. Thus the bloom of a lily contains six stamens (the microsporangia) which produce microspores which develop into pollen grains (the microgametophytes), and three fused carpels which produce integumented megasporangia (ovules) each of which produces a megaspore which develops within the megasporangium to produce the megagametophyte. In other plants, such as hazel, some flowers have only stamens, others only carpels, but the same plant (i.e. sporophyte) has both kinds of flower and and so is monoecious.

      

      Flowers of European holly, a dioecious species: male above, female below (leaves cut to prove flowers more clearly)

    • Megasporangia and microsporangia occur on different sporophytes, which are then chosen dioecious.
      An individual tree of the European holly (Ilex aquifolium) produces either 'male person' flowers which take simply functional stamens (microsporangia) producing microspores which develop into pollen grains (microgametophytes) or 'female' flowers which have only functional carpels producing integumented megasporangia (ovules) that contain a megaspore that develops into a multicellular megagametophyte.

There are some correlations betwixt these variations, but they are just that, correlations, and not absolute. For example, in flowering plants, microspores ultimately produce microgametes (sperm) and megaspores ultimately produce megagametes (eggs). However, in ferns and their allies there are groups with undifferentiated spores but differentiated gametophytes. For example, the fern Ceratopteris thalictrioides has spores of simply one kind, which vary continuously in size. Smaller spores tend to germinate into gametophytes which produce only sperm-producing antheridia.^[27]

A complex life cycle [edit]

Graphic referred in text.

The diagram shows the alternation of generations in a species which is heteromorphic, sporophytic, oogametic, dioicous, heterosporic and dioecious. A seed establish example might exist a willow tree (most species of the genus Salix are dioecious).^[28] Starting in the centre of the diagram, the processes involved are:

• An immobile egg, contained in the archegonium, fuses with a mobile sperm, released from an antheridium. The resulting zygote is either 'male' or 'female'.
  • A 'male' zygote develops past mitosis into a microsporophyte, which at maturity produces one or more microsporangia. Microspores develop within the microsporangium by meiosis.
    In a willow (similar all seed plants) the zygote first develops into an embryo microsporophyte inside the ovule (a megasporangium enclosed in one or more protective layers of tissue known every bit integument). At maturity, these structures become the seed. Afterward the seed is shed, germinates and grows into a mature tree. A 'male person' willow tree (a microsporophyte) produces flowers with only stamens, the anthers of which are the microsporangia.
  • Microspores germinate producing microgametophytes; at maturity one or more antheridia are produced. Sperm develop within the antheridia.
    In a willow, microspores are not liberated from the anther (the microsporangium), only develop into pollen grains (microgametophytes) within it. The whole pollen grain is moved (east.g. by an insect or by the wind) to an ovule (megagametophyte), where a sperm is produced which moves down a pollen tube to attain the egg.
  • A 'female' zygote develops by mitosis into a megasporophyte, which at maturity produces 1 or more megasporangia. Megaspores develop inside the megasporangium; typically one of the four spores produced by meiosis gains bulk at the expense of the remaining three, which disappear.
    'Female' willow trees (megasporophytes) produce flowers with but carpels (modified leaves that bear the megasporangia).
  • Megaspores germinate producing megagametophytes; at maturity ane or more archegonia are produced. Eggs develop inside the archegonia.
    The carpels of a willow produce ovules, megasporangia enclosed in integuments. Within each ovule, a megaspore develops by mitosis into a megagametophyte. An archegonium develops within the megagametophyte and produces an egg. The whole of the gametophytic 'generation' remains inside the protection of the sporophyte except for pollen grains (which have been reduced to just three cells contained within the microspore wall).

Life cycles of different institute groups [edit]

The term "plants" is taken here to mean the Archaeplastida, i.east. the glaucophytes, red and green algae and state plants.

Alternation of generations occurs in almost all multicellular red and green algae, both freshwater forms (such equally Cladophora) and seaweeds (such as Ulva). In virtually, the generations are homomorphic (isomorphic) and costless-living. Some species of red algae accept a complex triphasic alternation of generations, in which there is a gametophyte phase and two singled-out sporophyte phases. For further information, see Cherry-red algae: Reproduction.

Land plants all have heteromorphic (anisomorphic) alternation of generations, in which the sporophyte and gametophyte are distinctly unlike. All bryophytes, i.e. liverworts, mosses and hornworts, have the gametophyte generation as the virtually conspicuous. As an illustration, consider a monoicous moss. Antheridia and archegonia develop on the mature found (the gametophyte). In the presence of water, the biflagellate sperm from the antheridia swim to the archegonia and fertilisation occurs, leading to the production of a diploid sporophyte. The sporophyte grows up from the archegonium. Its torso comprises a long stalk topped past a sheathing within which spore-producing cells undergo meiosis to grade haploid spores. Most mosses rely on the wind to disperse these spores, although Splachnum sphaericum is entomophilous, recruiting insects to disperse its spores. For further information, see Liverwort: Life cycle, Moss: Life cycle, Hornwort: Life cycle.

• 

  Diagram of alternation of generations in liverworts.

• 

  Moss life cycle diagram

• 

  Hornwort life cycle diagram

In ferns and their allies, including clubmosses and horsetails, the conspicuous plant observed in the field is the diploid sporophyte. The haploid spores develop in sori on the underside of the fronds and are dispersed by the wind (or in some cases, past floating on water). If conditions are correct, a spore volition germinate and grow into a rather camouflaged plant body called a prothallus. The haploid prothallus does not resemble the sporophyte, and as such ferns and their allies have a heteromorphic alternation of generations. The prothallus is short-lived, simply carries out sexual reproduction, producing the diploid zygote that then grows out of the prothallus as the sporophyte. For further information, see Fern: Life cycle.

• 

  Diagram of alternation of generations in ferns.

• 

  A gametophyte (prothallus) of Dicksonia sp.

• 

  A sporophyte of Dicksonia antarctica.

• 

  The underside of a Dicksonia antarctica frond showing the sori, or spore-producing structures.

In the spermatophytes, the seed plants, the sporophyte is the dominant multicellular phase; the gametophytes are strongly reduced in size and very different in morphology. The entire gametophyte generation, with the sole exception of pollen grains (microgametophytes), is contained within the sporophyte. The life cycle of a dioecious angiosperm (angiosperm), the willow, has been outlined in some item in an before section (A complex life cycle). The life cycle of a gymnosperm is similar. However, flowering plants have in addition a phenomenon chosen 'double fertilization'. Two sperm nuclei from a pollen grain (the microgametophyte), rather than a single sperm, enter the archegonium of the megagametophyte; one fuses with the egg nucleus to form the zygote, the other fuses with two other nuclei of the gametophyte to form 'endosperm', which nourishes the developing embryo. For further information, see Double fertilization.

Development of the dominant diploid phase [edit]

It has been proposed that the basis for the emergence of the diploid phase of the life cycle (sporophyte) every bit the dominant phase (e.g. as in vascular plants) is that diploidy allows masking of the expression of deleterious mutations through genetic complementation.^{[29] [30]} Thus if i of the parental genomes in the diploid cells contained mutations leading to defects in one or more cistron products, these deficiencies could be compensated for by the other parental genome (which nevertheless may have its own defects in other genes). As the diploid phase was becoming predominant, the masking effect probable allowed genome size, and hence data content, to increase without the constraint of having to improve accuracy of Deoxyribonucleic acid replication. The opportunity to increment data content at low cost was advantageous because it permitted new adaptations to be encoded. This view has been challenged, with bear witness showing that choice is no more constructive in the haploid than in the diploid phases of the lifecycle of mosses and angiosperms.^[31]

• 

  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

Similar processes in other organisms [edit]

Rhizaria [edit]

Life wheel of Foraminifera showing alternation of generations.

Some organisms currently classified in the clade Rhizaria and thus not plants in the sense used hither, exhibit alternation of generations. Near Foraminifera undergo a heteromorphic alternation of generations between haploid gamont and diploid agamont forms. The single-celled haploid organism is typically much larger than the diploid organism.

Fungi [edit]

Fungal mycelia are typically haploid. When mycelia of different mating types meet, they produce two multinucleate ball-shaped cells, which join via a "mating span". Nuclei move from one mycelium into the other, forming a heterokaryon (significant "different nuclei"). This process is chosen plasmogamy . Bodily fusion to form diploid nuclei is called karyogamy , and may not occur until sporangia are formed. Karogamy produces a diploid zygote, which is a short-lived sporophyte that soon undergoes meiosis to class haploid spores. When the spores germinate, they develop into new mycelia.

Slime moulds [edit]

The life bike of slime moulds is very like to that of fungi. Haploid spores germinate to grade swarm cells or myxamoebae . These fuse in a process referred to as plasmogamy and karyogamy to course a diploid zygote. The zygote develops into a plasmodium, and the mature plasmodium produces, depending on the species, one to many fruiting bodies containing haploid spores.

Animals [edit]

Alternation between a multicellular diploid and a multicellular haploid generation is never encountered in animals.^[32] In some animals, there is an alternation between parthenogenic and sexually reproductive phases (heterogamy). Both phases are diploid. This has sometimes been chosen "alternation of generations",^[33] merely is quite different. In another animals, such as hymenopterans, males are haploid and females diploid, but this is always the case rather than there being an alternation betwixt singled-out generations.

See also [edit]

• Evolutionary history of plants#life cycles – Origin and diversification of plants through geologic time: Evolutionary origin of the alternation of phases
• Ploidy – Number of sets of chromosomes in a jail cell
• Biological life cycle – Series of stages of an organism
• Apomixis – Replacement of the normal sexual reproduction past asexual reproduction, without fertilization

Notes and references [edit]

1. ^ "alternation of generations | Definition & Examples". Encyclopedia Britannica . Retrieved 2021-02-25 .
2. ^ Thomas, R.J.; Stanton, D.S.; Longendorfer, D.H. & Farr, 1000.E. (1978), "Physiological evaluation of the nutritional autonomy of a hornwort sporophyte", Botanical Gazette, 139 (iii): 306–311, doi:x.1086/337006, S2CID 84413961
3. ^ Glime, J.M. (2007), Bryophyte Ecology: Vol. 1 Physiological Environmental (PDF), Michigan Technological University and the International Association of Bryologists, retrieved 2013-03-04
4. ^ ^{a b} Kerp, H.; Trewin, N.H. & Hass, H. (2003), "New gametophytes from the Lower Devonian Rhynie Chert", Transactions of the Royal Society of Edinburgh: Earth Sciences, 94 (four): 411–428, doi:10.1017/S026359330000078X, S2CID 128629425
5. ^ Kluge, Arnold Thousand.; Strauss, Richard E. (1985). "Ontogeny and Systematics". Annual Review of Ecology and Systematics. xvi: 247–268. doi:x.1146/annurev.es.xvi.110185.001335. ISSN 0066-4162. JSTOR 2097049.
6. ^ Taylor, Kerp & Hass 2005
7. ^ ""Plant Science 4 U". Retrieved 5 July 2016.
8. ^ ^{a b} Bateman & Dimichele 1994, p. 403
9. ^ ^{a b} Stewart & Rothwell 1993
10. ^ ^{a b c d east} Haig, David (2008), "Homologous versus antithetic alternation of generations and the origin of sporophytes" (PDF), The Botanical Review, 74 (three): 395–418, doi:x.1007/s12229-008-9012-x, S2CID 207403936, retrieved 2014-08-17
11. ^ Svedelius, Nils (1927), "Alternation of Generations in Relation to Reduction Segmentation", Botanical Gazette, 83 (4): 362–384, doi:ten.1086/333745, JSTOR 2470766, S2CID 84406292
12. ^ Hofmeister, West. (1851), Vergleichende Untersuchungen der Keimung, Entfaltung und Fruchtbildildiung höherer Kryptogamen (Moose, Farne, Equisetaceen, Rhizocarpeen und Lycopodiaceen) und der Samenbildung der Coniferen (in German), Leipzig: F. Hofmeister, retrieved 2014-08-17 . Translated as Currey, Frederick (1862), On the germination, development, and fructification of the higher Cryptogamia, and on the fructification of the Coniferæ, London: Robert Hardwicke, retrieved 2014-08-17
13. ^ Feldmann, J. & Feldmann, Thousand. (1942), "Recherches sur les Bonnemaisoniacées et leur alternance de generations" (PDF), Ann. Sci. Natl. Bot., Series 11 (in French), iii: 75–175, archived from the original (PDF) on 2014-08-xix, retrieved 2013-10-07 , p. 157
14. ^ ^{a b} Feldmann, J. (1972), "Les problèmes actuels de l'alternance de génerations chez les Algues", Bulletin de la Société Botanique de French republic (in French), 119: seven–38, doi:ten.1080/00378941.1972.10839073
15. ^ Schopfer, P.; Mohr, H. (1995). "Physiology of Development". Found physiology. Berlin: Springer. pp. 288–291. ISBN978-3-540-58016-four.
16. ^ Unless otherwise indicated, the material in the whole of this section is based on Foster & Gifford 1974, Sporne 1974a and Sporne 1974b.
17. ^ Guiry & Guiry 2008
18. ^ Bateman & Dimichele 1994, p. 347
19. ^ ^{a b} Shyam 1980
20. ^ Watson 1981, p. 2
21. ^ Kirby 2001
22. ^ Watson 1981, p. 33
23. ^ Bong & Hemsley 2000, p. 104
24. ^ Watson 1981, pp. 425–6
25. ^ Watson 1981, pp. 287–8
26. ^ Sporne 1974a, pp. 17–21.
27. ^ ^{a b} Bateman & Dimichele 1994, pp. 350–ane
28. ^ Chisholm, Hugh, ed. (1911). "Willow". Encyclopædia Britannica. Vol. 28 (11th ed.). Cambridge University Press. pp. 688–689.
29. ^ Bernstein, H.; Byers, Thousand.South. & Michod, R.E. (1981), "Evolution of sexual reproduction: Importance of Dna repair, complementation, and variation", The American Naturalist, 117 (4): 537–549, doi:ten.1086/283734, S2CID 84568130
30. ^ Michod, R.E. & Gayley, T.W. (1992), "Masking of mutations and the evolution of sex", The American Naturalist, 139 (iv): 706–734, doi:10.1086/285354, S2CID 85407883
31. ^ Szövényi, Péter; Ricca, Mariana; Hock, Zsófia; Shaw, Jonathan A.; Shimizu, Kentaro K. & Wagner, Andreas (2013), "Option is no more efficient in haploid than in diploid life stages of an angiosperm and a moss", Molecular Biology and Development, 30 (8): 1929–39, doi:10.1093/molbev/mst095, PMID 23686659
32. ^ Barnes et al. 2001, p. 321
33. ^ Scott 1996, p. 35

Bibliography [edit]

• Barnes, R.S.K.; Calow, P.; Olive, P.J.W.; Golding, D.W. & Spicer, J.I. (2001), The Invertebrates: a synthesis, Oxford; Malden, MA: Blackwell, ISBN978-0-632-04761-one
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Source: https://en.wikipedia.org/wiki/Alternation_of_generations

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