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In plants, spores are usually haploid and unicellular and are produced by meiosis in the sporangium of a diploid sporophyte. In some rare cases, diploid spore is also produced in some algae, or fungi. [6]
In meiotic sporogenesis, a diploid spore mother cell within the sporangium undergoes meiosis, producing a tetrad of haploid spores. In organisms that are heterosporous, two types of spores occur: Microsporangia produce male microspores, and megasporangia produce female megaspores. In megasporogenesis, often three of the four spores degenerate ...
The sporangium forms on the sporangiophore and contains haploid nuclei and cytoplasm. [3] Spores are formed in the sporangiophore by encasing each haploid nucleus and cytoplasm in a tough outer membrane. During asexual reproduction, these spores are dispersed via wind and germinate into haploid hyphae. [4]
Haploid spores germinate to form swarm cells or myxamoebae. These fuse in a process referred to as plasmogamy and karyogamy to form a diploid zygote. The zygote develops into a plasmodium, and the mature plasmodium produces, depending on the species, one to many fruiting bodies containing haploid spores.
Diagram showing the alternation of generations between a diploid sporophyte (bottom) and a haploid gametophyte (top) A sporophyte (/ ˈ s p ɔːr. ə ˌ f aɪ t /) is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase.
The gametophyte generation is haploid, and produces gametes by mitosis; the sporophyte generation is diploid and produces spores by meiosis. Polyploidy is the result of whole-genome duplication during the evolution of species.
Typically, a single ascus will contain eight ascospores (or octad). The eight spores are produced by meiosis followed by a mitotic division. Two meiotic divisions turn the original diploid zygote nucleus into four haploid ones. That is, the single original diploid cell from which the whole process begins contains two complete sets of chromosomes.
During vegetative growth that ordinarily occurs when nutrients are abundant, S. cerevisiae reproduces by mitosis as either haploid or diploid cells. However, when starved, diploid cells undergo meiosis to form haploid spores. [13] Mating occurs when haploid cells of opposite mating type, MATa and MATα, come into contact.