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Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, and some gymnosperms and closely related plants do so. [2] Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. [3] Many protists take the form of single-celled flagellates. Flagella are generally used for propulsion ...
[3] Gametes of both mating individuals can be the same size and shape, a condition known as isogamy. By contrast, in the majority of species, the gametes are of different sizes, a condition known as anisogamy or heterogamy that applies to humans and other mammals. The human ovum has approximately 100,000 times the volume of a single human sperm ...
Chiasmata play a crucial role in correctly segregating the chromosomes during meiosis I to maintain correct ploidy; when chiasmata fail to form, it typically results in aneuploidy and nonviable gametes. [2] However, some species have been found to employ alternative methods to segregate chromosomes. [5]
Gametogenesis is the formation or production of gametes (taking place during meiosis). The development and maturation of sex cells also takes place during meiosis. Gametogenesis is also the process of formation in male and female gametes that occur in the gonads (ovary and testis). Both male and female produce gametes.
Note 1] Some isogamous species have more than two mating types, but the number is usually lower than ten. In some extremely rare cases, such as in some basidiomycete species, a species can have thousands of mating types. [7] Under the strict definition of isogamy, fertilization occurs when two gametes fuse to form a zygote. [8]
Automixis [1] is the fusion of (typically haploid) nuclei or gametes derived from the same individual. [2] The term covers several reproductive mechanisms, some of which are parthenogenetic. [3] Diploidy might be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed.
[3] [4] There are exceptions, such as the opiliones that have immobile sperm. [5] Oogamy is found in all land plants, [6] and in some red algae, brown algae and green algae. [7]: 309 Oogamy is favored in land plants because only one gamete has to travel through harsh environments outside the plant. [7]: 376 Oogamy is also present in oomycetes. [8]
For example, some brown alga (Phaeophyceae) reproduce by producing multi-flagellated male and female gametes that recombine to form the diploid sporangia. [2] Zoids are primarily found in some protists, diatoms, [1] green alga, brown alga, [3] non-vascular plants, [4] and a few vascular plants (ferns, [1] cycads, [5] and Ginkgo biloba [6]).