haploid

Examples of haploid in the following topics:

• Life Cycles of Sexually Reproducing Organisms

  • There is no multicellular haploid life stage.
  • Within haploid-dominant life cycles, the multicellular haploid stage is the most obvious life stage.
  • However, at some point in each type of life cycle, meiosis produces haploid cells that will fuse with the haploid cell of another organism.
  • The haploid multicellular stage produces specialized haploid cells by mitosis that fuse to form a diploid zygote.
  • The zygote undergoes meiosis to produce haploid spores.

• Ascomycota: The Sac Fungi

  • Most fungi belong to the Phylum Ascomycota, which uniquely forms of an ascus, a sac-like structure that contains haploid ascospores.
  • Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores .
  • In each ascus, two or more haploid ascospores fuse their nuclei in karyogamy.
  • The diploid nucleus gives rise to haploid nuclei by meiosis.
  • The haploid phase is the predominant phase of the life cycle.

• Introduction to Meiosis

  • Meiosis is the nuclear division of diploid cells into haploid cells, which is a necessary step in sexual reproduction.
  • Haploid cells contain one set of chromosomes.
  • Sexual reproduction is the production of haploid cells (gametes) and the fusion (fertilization) of two gametes to form a single, unique diploid cell called a zygote.
  • Haploid cells that are part of the sexual reproductive cycle are produced by a type of cell division called meiosis.
  • However, the starting nucleus is always diploid and the nuclei that result at the end of a meiotic cell division are haploid, so the resulting cells have half the chromosomes as the original.

• Meiosis II

  • During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes.
  • During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes.
  • Cytokinesis separates the two cells into four unique haploid cells.
  • At this point, the newly-formed nuclei are both haploid.
  • An animal cell with a diploid number of four (2n = 4) proceeds through the stages of meiosis to form four haploid daughter cells.

• Protist Life Cycles and Habitats

  • Some protists are unicellular in the haploid form and multicellular in the diploid form, which is a strategy also employed by animals.
  • Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations that is also used by plants.
  • Meiosis produces haploid spores within the sporangia.
  • Cells atop the stalk form an asexual fruiting body that contains haploid spores.
  • The sporangium forms haploid spores through meiosis, after which the spores disseminate, germinate, and begin the life cycle anew.

• Life Cycle of a Conifer

  • The pollen tube develops slowly as the generative cell in the pollen grain divides into two haploid sperm cells by mitosis.
  • At fertilization, one of the sperm cells will finally unite its haploid nucleus with the haploid nucleus of an egg cell.

• Chromalveolata: Stramenopiles

  • 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.
  • In the brown algae genus Laminaria, haploid spores develop into multicellular gametophytes, which produce haploid gametes that combine to produce diploid organisms that then become multicellular organisms with a different structure from the haploid form .
  • Several species of brown algae, such as the Laminaria shown here, have evolved life cycles in which both the haploid (gametophyte) and diploid (sporophyte) forms are multicellular.

• Meiosis I

  • In meiosis I, the first round of meiosis, homologous chromosomes exchange DNA and the diploid cell is divided into two haploid cells.
  • Given these two mechanisms, it is highly unlikely that any two haploid cells resulting from meiosis will have the same genetic composition .
  • Two haploid cells are the end result of the first meiotic division.
  • The cells are haploid because at each pole there is just one of each pair of the homologous chromosomes.

• Gametogenesis (Spermatogenesis and Oogenesis)

  • Spermatogenesis and oogenesis are both forms of gametogenesis, in which a diploid gamete cell produces haploid sperm and egg cells, respectively.
  • At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte.
  • This haploid cell must go through another meiotic cell division.
  • During spermatogenesis, four sperm result from each primary spermatocyte, which divides into two haploid secondary spermatocytes; these cells will go through a second meiotic division to produce four spermatids.

• Sporophytes and Gametophytes in Seedless Plants

  • Inside the multicellular sporangia, the diploid sporocytes, or mother cells, produce haploid spores by meiosis, where the 2n chromosome number is reduced to 1n (note that many plant sporophytes are polyploid: for example, durum wheat is tetraploid, bread wheat is hexaploid, and some ferns are 1000-ploid).
  • When the haploid spore germinates in a hospitable environment, it generates a multicellular gametophyte by mitosis.
  • Gametangia (singular, gametangium) are organs observed on multicellular haploid gametophytes.