alternation of generation

(noun)

the life cycle of plants with a multicellular sporophyte, which is diploid, that alternates with a multicellular gametophyte, which is haploid

Related Terms

  • pseudoelater
  • gemmae
  • desiccation tolerance

Examples of alternation of generation in the following topics:

  • Life Cycles of Sexually Reproducing Organisms

    • The main categories of sexual life cycles in eukaryotic organisms are: diploid-dominant, haploid-dominant, and alternation of generations.
    • There are three main categories of life cycles in eukaryotic organisms: diploid-dominant, haploid-dominant, and alternation of generations.
    • Species with alternation of generations have both haploid and diploid multicellular organisms as part of their life cycle.
    • Although all plants utilize some version of the alternation of generations, the relative size of the sporophyte and the gametophyte and the relationship between them vary greatly.
    • The germ cells are generated early in the development of the zygote.
  • Seedless Vascular Plants

    • More than 260,000 species of tracheophytes represent more than 90 percent of the earth's vegetation.
    • Although seedless vascular plants have evolved to spread to all types of habitats, they still depend on water during fertilization, as the sperm must swim on a layer of moisture to reach the egg.
    • The life cycle of seedless vascular plants is an alternation of generations, where the diploid sporophyte alternates with the haploid gametophyte phase.
    • Throughout plant evolution, there is a clear reversal of roles in the dominant phase of the life cycle.
    • This life cycle of a fern shows alternation of generations with a dominant sporophyte stage.
  • Liverworts and Hornworts

    • Thus, the life cycle of liverworts follows the pattern of alternation of generations .
    • The life cycle of hornworts also follows the general pattern of alternation of generations and has a similar life cycle to liverworts.
    • The haploid spores germinate and produce the next generation of gametophytes .
    • The life cycle of a typical liverwort follows the pattern of alternation of generations.
    • Both follow the pattern of alternation of generations.
  • Plant Adaptations to Life on Land

    • Four major adaptations are found in all terrestrial plants: the alternation of generations, a sporangium in which the spores are formed, a gametangium that produces haploid cells, and apical meristem tissue in roots and shoots.
    • Alternation of generations describes a life cycle in which an organism has both haploid and diploid multicellular stages (n represents the number of copies of chromosomes) .
    • Most plants exhibit alternation of generations, which is described as haplodiplodontic.
    • This distinguishing feature of land plants gave the group its alternate name of embryophytes.
    • Plants exhibit an alternation of generations between a 1n gametophyte and 2n sporophyte.
  • Mosses

    • These structures are precursors of roots.
    • They originate from the base of the gametophyte, but are not the major route for the absorption of water and minerals.
    • The moss life cycle follows the pattern of alternation of generations .
    • A structure called a peristome increases the spread of spores after the tip of the capsule falls off at dispersal.
    • The alternation of generations cycle begins when the gametophyte germinates from a haploid spore and forms a protonema.
  • Chromalveolata: Stramenopiles

    • The unifying feature of this group is the presence of a textured, or "hairy," flagellum.
    • Their characteristic gold color results from their extensive use of carotenoids, a group of photosynthetic pigments that are generally yellow or orange in color.
    • A variety of algal life cycles exists, but the most complex is alternation of generations in which both haploid and diploid stages involve multicellularity.
    • In humans, haploid gametes produced by meiosis (sperm and egg) combine in fertilization to generate a diploid zygote that undergoes many rounds of mitosis to produce a multicellular embryo and then a fetus.
    • Terrestrial plants also have evolved alternation of generations.
  • Basidiomycota: The Club Fungi

    • The lifecycle of basidiomycetes includes alternation of generations .
    • Spores are generally produced through sexual reproduction, rather than asexual reproduction.
    • The haploid nuclei migrate into basidiospores, which germinate and generate monokaryotic hyphae.
    • Eventually, the secondary mycelium generates a basidiocarp, which is a fruiting body that protrudes from the ground; this is what we think of as a mushroom.
    • The lifecycle of a basidiomycete alternates generation with a prolonged stage in which two nuclei (dikaryon) are present in the hyphae.
  • Characteristics of Fungi

    • While scientists have identified about 100,000 species of fungi, this is only a fraction of the 1.5 million species of fungus probably present on earth.
    • Some fungal organisms multiply only asexually, whereas others undergo both asexual reproduction and sexual reproduction with alternation of generations.
    • The roots of the plant connect with the underground parts of the fungus forming mycorrhizae.
    • Through mycorrhizae, the fungus and plant exchange nutrients and water, greatly aiding the survival of both species Alternatively, lichens are an association between a fungus and its photosynthetic partner (usually an alga).
    • In humans, fungal infections are generally considered challenging to treat.
  • Alternatives to Dominance and Recessiveness

    • Mendel's experiments with pea plants suggested that: (1) two "units" or alleles exist for every gene; (2) alleles maintain their integrity in each generation (no blending); and (3) in the presence of the dominant allele, the recessive allele is hidden and makes no contribution to the phenotype.
    • An example of codominance is the MN blood groups of humans.
    • Alternatively, one mutant allele can be dominant over all other phenotypes, including the wild type.
    • Example of a mutant allele interfering with the function of a wild-type gene
    • Discuss incomplete dominance, codominance, and multiple alleles as alternatives to dominance and recessiveness
  • RNA Splicing

    • Alternative splicing is a process that occurs during gene expression and allows for the production of multiple proteins (protein isoforms) from a single gene coding.
    • This results in what is called alternative splicing .
    • The pattern of splicing and production of alternatively-spliced messenger RNA is controlled by the binding of regulatory proteins (trans-acting proteins that contain the genes) to cis-acting sites that are found on the pre-RNA.
    • Proteins that are translated from alternatively-spliced messenger RNAs differ in the sequence of their amino acids which results in altered function of the protein.
    • Alternative splicing is a common process that occurs in eukaryotes; most of the multi-exonic genes in humans are spliced alternatively.
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