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.

• Complementation

  • When this occurs, each strain's haploid supplies a wild-type allele to "complement" the mutated allele of the other strain's haploid, causing the offspring to have heterozygous mutations in all related genes.
  • In other words, if the combination of two haploid genomes containing different recessive mutations yields a mutant phenotype, then there are three possibilities: Mutations occur in the same gene; One mutation affects the expression of the other; One mutation may result in an inhibitory product.
  • If the combination of two haploid genomes containing different recessive mutations yields the wild type phenotype, then the mutations must be in different genes.

• 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.

• 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.

• Spermatogenesis

  • *Each primary spermatocyte then moves into the adluminal compartment of the seminiferous tubules, duplicates its DNA, and subsequently undergoes meiosis I to produce two haploid secondary spermatocytes
  • *Secondary spermatocytes later divide into haploid spermatids.
  • Secondary spermatocytes produced earlier rapidly enter meiosis II and divide to produce haploid spermatids.