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Reproductive spores are generally the result of cell division, most commonly meiosis (e.g. in plant sporophytes). Sporic meiosis is needed to complete the sexual life cycle of the organisms using it. In some cases, sporogenesis occurs via mitosis (e.g. in some fungi and algae). Mitotic sporogenesis is a form of asexual reproduction.
Some cells divide by budding (for example baker's yeast), resulting in a "mother" and a "daughter" cell that is initially smaller than the parent. Budding is also known on a multicellular level; an animal example is the hydra, [10] which reproduces by budding. The buds grow into fully matured individuals which eventually break away from the ...
The egg cells, depending on the species may be produced without meiosis (apomictically) or by one of the several automictic mechanisms. [citation needed] A related phenomenon, polyembryony is a process that produces multiple clonal offspring from a single egg cell. This is known in some hymenopteran parasitoids and in Strepsiptera. [11]
Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. [33] One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies ; presumably, this is the default reproductive mode of all species in this insect order. [ 34 ]
Spores are usually haploid and grow into mature haploid individuals through mitotic division of cells (Urediniospores and Teliospores among rusts are dikaryotic). Dikaryotic cells result from the fusion of two haploid gamete cells. Among sporogenic dikaryotic cells, karyogamy (the fusion of the two haploid nuclei) occurs to produce a diploid cell.
Ochrophytes are eukaryotic organisms composed of cells that are either naked or covered by scales, lorica or a cell wall. They can be single-celled , colonial , coenocytic or multicellular . Some Phaeophyceae (brown algae, seaweeds) develop as large multicellular thalli with differentiated tissues . [ 7 ]
The partitioning apparatus of the mitotic-like cell cycle the cells used to replicate independently would then pull each set of chromosomes to one side of the cell, still bound by centromeres. These centromeres would prevent their replication in subsequent division, resulting in four daughter cells with one copy of one of the two original pox ...
In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5]