Life Cycles

• observed in some algae, cellular slime molds, fungi
• fusion of two haploid gametes (produced by haploid individuals, using mitosis) --> zygote undergoes meiosis to create haploid spore nuclei
• unique feature to fungi: no gametes; plasmogamy not immediately followed by karyogamy

• plasmogamy --> dikaryon state --> fruiting structures form --> in which karyogamy occurs
• the spores are not released into the environment; liquid water not needed for fertilization (except for the chytrids, which have flagellated gametes)
• karyogamy occurs long after plasmogamy has occured

• the fusion of the nuclei in fungi
• occurs in the fruiting structures
• occurs long after plasmogamy; the time between them depends on the species

• fusion of two hyphae from two different individuals
• of two mating types (+/-)
• creates a dikaryon state (n+n; two distinct haploid nuclei)

• observed in animals
• produce haploid gametes using meiosis --> fuse together (syngamy/fertilization) to produce a diploid zygote --> undergoes mitosis to produce a multicellular adult

• oberved in some algae and in multicellular plants
• typical of alternation of generations
• two distinct different adults in the cylce

• multicellular haploid adult (gametophyte)
• multicellular diploid adult (sporophyte)

sporophyte cells undergo meiosis --> produce haploid spores --> undergo mitosis to produce multicellular gametophyte --> undergo mitosis to produce gametes --> syngamy to form zygote --> undergoes mitosis to produce sporophyte

• in both the zygotic and sporic life cycles can give rise directly to adult stages
• long-lived
• do not fuse with another spore
• in fungi - spores are produced both mitotically and meiotically
• in plants - spores are produced by meiosis (in sporphyte adult)

• must fuse with another gamete to produce zygote
• short-lived
• in plants (sporic life cycle) - gametes are produced by mitosis (in gametophyte adult)
• in animals (gametic life cycle) - gametes are produced by meiosis